Moves sweep phase out of stoptheworld by adding
background sweeper goroutine and lazy on-demand sweeping.
It turned out to be somewhat trickier than I expected,
because there is no point in time when we know size of live heap
nor consistent number of mallocs and frees.
So everything related to next_gc, mprof, memstats, etc becomes trickier.
At the end of GC next_gc is conservatively set to heap_alloc*GOGC,
which is much larger than real value. But after every sweep
next_gc is decremented by freed*GOGC. So when everything is swept
next_gc becomes what it should be.
For mprof I had to introduce 3-generation scheme (allocs, revent_allocs, prev_allocs),
because by the end of GC we know number of frees for the *previous* GC.
Significant caution is required to not cross yet-unknown real value of next_gc.
This is achieved by 2 means:
1. Whenever I allocate a span from MCentral, I sweep a span in that MCentral.
2. Whenever I allocate N pages from MHeap, I sweep until at least N pages are
returned to heap.
This provides quite strong guarantees that heap does not grow when it should now.
http-1
allocated 7036 7033 -0.04%
allocs 60 60 +0.00%
cputime 51050 46700 -8.52%
gc-pause-one 34060569 1777993 -94.78%
gc-pause-total 2554 133 -94.79%
latency-50 178448 170926 -4.22%
latency-95 284350 198294 -30.26%
latency-99 345191 220652 -36.08%
rss 101564416 101007360 -0.55%
sys-gc 6606832 6541296 -0.99%
sys-heap 88801280 87752704 -1.18%
sys-other 7334208 7405928 +0.98%
sys-stack 524288 524288 +0.00%
sys-total 103266608 102224216 -1.01%
time 50339 46533 -7.56%
virtual-mem 292990976 293728256 +0.25%
garbage-1
allocated 2983818 2990889 +0.24%
allocs 62880 62902 +0.03%
cputime 16480000 16190000 -1.76%
gc-pause-one 828462467 487875135 -41.11%
gc-pause-total 4142312 2439375 -41.11%
rss 1151709184 1153712128 +0.17%
sys-gc 66068352 66068352 +0.00%
sys-heap 1039728640 1039728640 +0.00%
sys-other 37776064 40770176 +7.93%
sys-stack 8781824 8781824 +0.00%
sys-total 1152354880 1155348992 +0.26%
time 16496998 16199876 -1.80%
virtual-mem 1409564672 1402281984 -0.52%
LGTM=rsc
R=golang-codereviews, sameer, rsc, iant, jeremyjackins, gobot
CC=golang-codereviews, khr
https://golang.org/cl/46430043
Currently windows crashes because early allocs in schedinit
try to allocate tiny memory blocks, but m->p is not yet setup.
I've considered calling procresize(1) earlier in schedinit,
but this refactoring is better and must fix the issue as well.
Fixes#7218.
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/54570045
There is more zeroing than I would like right now -
temporaries used for the new map and channel runtime
calls need to be eliminated - but it will do for now.
This CL only has an effect if you are building with
GOEXPERIMENT=precisestack ./all.bash
(or make.bash). It costs about 5% in the overall time
spent in all.bash. That number will come down before
we make it on by default, but this should be enough for
Keith to try using the precise maps for copying stacks.
amd64 only (and it's not really great generated code).
TBR=khr, iant
CC=golang-codereviews
https://golang.org/cl/56430043
Introduces two-phase goroutine parking mechanism -- prepare to park, commit park.
This mechanism does not require backing mutex to protect wait predicate.
Use it in netpoll. See comment in netpoll.goc for details.
This slightly reduces contention between reader, writer and read/write io notifications;
and just eliminates a bunch of mutex operations from hotpaths, thus making then faster.
benchmark old ns/op new ns/op delta
BenchmarkTCP4ConcurrentReadWrite 2109 1945 -7.78%
BenchmarkTCP4ConcurrentReadWrite-2 1162 1113 -4.22%
BenchmarkTCP4ConcurrentReadWrite-4 798 755 -5.39%
BenchmarkTCP4ConcurrentReadWrite-8 803 748 -6.85%
BenchmarkTCP4Persistent 9411 9240 -1.82%
BenchmarkTCP4Persistent-2 5888 5813 -1.27%
BenchmarkTCP4Persistent-4 4016 3968 -1.20%
BenchmarkTCP4Persistent-8 3943 3857 -2.18%
R=golang-codereviews, mikioh.mikioh, gobot, iant, rsc
CC=golang-codereviews, khr
https://golang.org/cl/45700043
Currently we collect (add) all roots into a global array in a single-threaded GC phase.
This hinders parallelism.
With this change we just kick off parallel for for number_of_goroutines+5 iterations.
Then parallel for callback decides whether it needs to scan stack of a goroutine
scan data segment, scan finalizers, etc. This eliminates the single-threaded phase entirely.
This requires to store all goroutines in an array instead of a linked list
(to allow direct indexing).
This CL also removes DebugScan functionality. It is broken because it uses
unbounded stack, so it can not run on g0. When it was working, I've found
it helpless for debugging issues because the two algorithms are too different now.
This change would require updating the DebugScan, so it's simpler to just delete it.
With 8 threads this change reduces GC pause by ~6%, while keeping cputime roughly the same.
garbage-8
allocated 2987886 2989221 +0.04%
allocs 62885 62887 +0.00%
cputime 21286000 21272000 -0.07%
gc-pause-one 26633247 24885421 -6.56%
gc-pause-total 873570 811264 -7.13%
rss 242089984 242515968 +0.18%
sys-gc 13934336 13869056 -0.47%
sys-heap 205062144 205062144 +0.00%
sys-other 12628288 12628288 +0.00%
sys-stack 11534336 11927552 +3.41%
sys-total 243159104 243487040 +0.13%
time 2809477 2740795 -2.44%
R=golang-codereviews, rsc
CC=cshapiro, golang-codereviews, khr
https://golang.org/cl/46860043
Instead of a per-goroutine stack of defers for all sizes,
introduce per-P defer pool for argument sizes 8, 24, 40, 56, 72 bytes.
For a program that starts 1e6 goroutines and then joins then:
old: rss=6.6g virtmem=10.2g time=4.85s
new: rss=4.5g virtmem= 8.2g time=3.48s
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/42750044
Currently for 2-word blocks we set the flag to clear the flag. Makes no sense.
In particular on 32-bits we call memclr always.
R=golang-codereviews, dave, iant
CC=golang-codereviews, khr, rsc
https://golang.org/cl/41170044
Example of output:
goroutine 4 [sleep for 3 min]:
time.Sleep(0x34630b8a000)
src/pkg/runtime/time.goc:31 +0x31
main.func·002()
block.go:16 +0x2c
created by main.main
block.go:17 +0x33
Full program and output are here:
http://play.golang.org/p/NEZdADI3TdFixes#6809.
R=golang-codereviews, khr, kamil.kisiel, bradfitz, rsc
CC=golang-codereviews
https://golang.org/cl/50420043
The spans array is allocated in runtime·mallocinit. On a
32-bit system the number of entries in the spans array is
MaxArena32 / PageSize, which (2U << 30) / (1 << 12) == (1 << 19).
So we are allocating an array that can hold 19 bits for an
index that can hold 20 bits. According to the comment in the
function, this is intentional: we only allocate enough spans
(and bitmaps) for a 2G arena, because allocating more would
probably be wasteful.
But since the span index is simply the upper 20 bits of the
memory address, this scheme only works if memory addresses are
limited to the low 2G of memory. That would be OK if we were
careful to enforce it, but we're not. What we are careful to
enforce, in functions like runtime·MHeap_SysAlloc, is that we
always return addresses between the heap's arena_start and
arena_start + MaxArena32.
We generally get away with it because we start allocating just
after the program end, so we only run into trouble with
programs that allocate a lot of memory, enough to get past
address 0x80000000.
This changes the code that computes a span index to subtract
arena_start on 32-bit systems just as we currently do on
64-bit systems.
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/49460043
record finalizers and heap profile info. Enables
removing the special bit from the heap bitmap. Also
provides a generic mechanism for annotating occasional
heap objects.
finalizers
overhead per obj
old 680 B 80 B avg
new 16 B/span 48 B
profile
overhead per obj
old 32KB 24 B + hash tables
new 16 B/span 24 B
R=cshapiro, khr, dvyukov, gobot
CC=golang-codereviews
https://golang.org/cl/13314053
On the plus side, we don't need to change the bits when mallocing
pointerless objects. On the other hand, we need to mark objects in the
free lists during GC. But the free lists are small at GC time, so it
should be a net win.
benchmark old ns/op new ns/op delta
BenchmarkMalloc8 40 33 -17.65%
BenchmarkMalloc16 45 38 -15.72%
BenchmarkMallocTypeInfo8 58 59 +0.85%
BenchmarkMallocTypeInfo16 63 64 +1.10%
R=golang-dev, rsc, dvyukov
CC=cshapiro, golang-dev
https://golang.org/cl/41040043
Adds the Pool type and docs, and use it in fmt.
This is a temporary implementation, until Dmitry
makes it fast.
Uses the API proposal from Russ in http://goo.gl/cCKeb2 but
adds an optional New field, as used in fmt and elsewhere.
Almost all callers want that.
Update #4720
R=golang-dev, rsc, cshapiro, iant, r, dvyukov, khr
CC=golang-dev
https://golang.org/cl/41860043
When enabled this new debugging mode will allocate objects on
their own page and never recycle memory addresses. This is an
essential tool to root cause a broad class of heap corruption.
R=golang-dev, dave, daniel.morsing, dvyukov, rsc, iant, cshapiro
CC=golang-dev
https://golang.org/cl/22060046
This change allows the garbage collector to examine stack
slots that are determined as live and containing a pointer
value by the garbage collector. This results in a mean
reduction of 65% in the number of stack slots scanned during
an invocation of "GOGC=1 all.bash".
Unfortunately, this does not yet allow garbage collection to
be precise for the stack slots computed as live. Pointers
confound the determination of what definitions reach a given
instruction. In general, this problem is not solvable without
runtime cost but some advanced cooperation from the compiler
might mitigate common cases.
R=golang-dev, rsc, cshapiro
CC=golang-dev
https://golang.org/cl/14430048
The code for call site-specific pointer bitmaps was not ready in time,
but the zeroing required without it is too expensive to use by default.
We will have to wait for precise collection of stack frames until Go 1.3.
The precise collection can be re-enabled by
GOEXPERIMENT=precisestack ./all.bash
but that will not be the default for a Go 1.2 build.
Fixes#6087.
R=golang-dev, jeremyjackins, dan.kortschak, r
CC=golang-dev
https://golang.org/cl/13677045
Currently lots of sys allocations are not accounted in any of XxxSys,
including GC bitmap, spans table, GC roots blocks, GC finalizer blocks,
iface table, netpoll descriptors and more. Up to ~20% can unaccounted.
This change introduces 2 new stats: GCSys and OtherSys for GC metadata
and all other misc allocations, respectively.
Also ensures that all XxxSys indeed sum up to Sys. All sys memory allocation
functions require the stat for accounting, so that it's impossible to miss something.
Also fix updating of mcache_sys/inuse, they were not updated after deallocation.
test/bench/garbage/parser before:
Sys 670064344
HeapSys 610271232
StackSys 65536
MSpanSys 14204928
MCacheSys 16384
BuckHashSys 1439992
after:
Sys 670064344
HeapSys 610271232
StackSys 65536
MSpanSys 14188544
MCacheSys 16384
BuckHashSys 3194304
GCSys 39198688
OtherSys 3129656
Fixes#5799.
R=rsc, dave, alex.brainman
CC=golang-dev
https://golang.org/cl/12946043
When searching for an allocated bit, flushptrbuf would search
backward in the bitmap word containing the bit of pointer
being looked-up before searching the span. This extra check
was not replicated in markonly which, instead, after not
finding an allocated bit for a pointer would directly look in
the span.
Using statistics generated from godoc, before this change span
lookups were, on average, more common than word lookups. It
was common for markonly to consult spans for one third of its
pointer lookups. With this change in place, what were
previously span lookups are overwhelmingly become by the word
lookups making the total number of span lookups a relatively
small fraction of the whole.
This change also introduces some statistics gathering about
lookups guarded by the CollectStats enum.
R=golang-dev, khr
CC=golang-dev
https://golang.org/cl/13311043
#pragma textflag and #pragma dataflag directives.
Update dataflag directives to use symbols instead of integer constants.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/13310043
the use of the flag, especially for objects which actually do have
pointers but we don't want the GC to scan them.
R=golang-dev, cshapiro
CC=golang-dev
https://golang.org/cl/13181045
GC acquires worldsema, which is a goroutine-level semaphore
which parks goroutines. g0 can not be parked.
Fixes#6193.
R=khr, khr
CC=golang-dev
https://golang.org/cl/12880045
Update the original change but do not read interface types in
the arguments area. Once the arguments area is zeroed as the
locals area is we can safely read interface type values there
too.
««« original CL description
undo CL 12785045 / 71ce80dc4195
This has broken the 32-bit builds.
««« original CL description
cmd/gc, runtime: use type information to scan interface values
R=golang-dev, rsc, dvyukov
CC=golang-dev
https://golang.org/cl/12785045
»»»
R=khr, golang-dev, khr
CC=golang-dev
https://golang.org/cl/13010045
»»»
R=khr, khr
CC=golang-dev
https://golang.org/cl/13073045
This has broken the 32-bit builds.
««« original CL description
cmd/gc, runtime: use type information to scan interface values
R=golang-dev, rsc, dvyukov
CC=golang-dev
https://golang.org/cl/12785045
»»»
R=khr, golang-dev, khr
CC=golang-dev
https://golang.org/cl/13010045
Originally the requirement was f(x) where f's argument is
exactly x's type.
CL 11858043 relaxed the requirement in a non-standard
way: f's argument must be exactly x's type or interface{}.
If we're going to relax the requirement, it should be done
in a way consistent with the rest of Go. This CL allows f's
argument to have any type for which x is assignable;
that's the same requirement the compiler would impose
if compiling f(x) directly.
Fixes#5368.
R=dvyukov, bradfitz, pieter
CC=golang-dev
https://golang.org/cl/12895043
Prior to this change, pointer maps encoded the disposition of
a word using a single bit. A zero signaled a non-pointer
value and a one signaled a pointer value. Interface values,
which are a effectively a union type, were conservatively
labeled as a pointer.
This change widens the logical element size of the pointer map
to two bits per word. As before, zero signals a non-pointer
value and one signals a pointer value. Additionally, a two
signals an iface pointer and a three signals an eface pointer.
Following other changes to the runtime, values two and three
will allow a type information to drive interpretation of the
subsequent word so only those interface values containing a
pointer value will be scanned.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12689046
The mutex, fdMutex, handles locking and lifetime of sysfd,
and serializes Read and Write methods.
This allows to strip 2 sync.Mutex.Lock calls,
2 sync.Mutex.Unlock calls, 1 defer and some amount
of misc overhead from every network operation.
On linux/amd64, Intel E5-2690:
benchmark old ns/op new ns/op delta
BenchmarkTCP4Persistent 9595 9454 -1.47%
BenchmarkTCP4Persistent-2 8978 8772 -2.29%
BenchmarkTCP4ConcurrentReadWrite 4900 4625 -5.61%
BenchmarkTCP4ConcurrentReadWrite-2 2603 2500 -3.96%
In general it strips 70-500 ns from every network operation depending
on processor model. On my relatively new E5-2690 it accounts to ~5%
of network op cost.
Fixes#6074.
R=golang-dev, bradfitz, alex.brainman, iant, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/12418043
Previously, all word aligned locations in the local variables
area were scanned as conservative roots. With this change, a
bitmap is generated describing the locations of pointer values
in local variables.
With this change the argument bitmap information has been
changed to only store information about arguments. The locals
member, has been removed. In its place, the bitmap data for
local variables is now used to store the size of locals. If
the size is negative, the magnitude indicates the size of the
local variables area.
R=rsc
CC=golang-dev
https://golang.org/cl/12328044
gcpc/gcsp are used by GC in similar situation.
gcpc/gcsp are also more stable than gp->sched,
because gp->sched is mutated by entersyscall/exitsyscall
in morestack and mcall. So it has higher chances of being inconsistent.
Also, rename gcpc/gcsp to syscallpc/syscallsp.
This is the same as reverted change 12250043
with save marked as textflag 7.
The problem was that if save calls morestack,
then subsequent lessstack spoils g->sched.pc/sp.
And that bad values were remembered in g->syscallpc/sp.
Entersyscallblock had the same problem,
but it was never triggered to date.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12478043
Break all 386 builders.
««« original CL description
runtime: use gcpc/gcsp during traceback of goroutines in syscalls
gcpc/gcsp are used by GC in similar situation.
gcpc/gcsp are also more stable than gp->sched,
because gp->sched is mutated by entersyscall/exitsyscall
in morestack and mcall. So it has higher chances of being inconsistent.
Also, rename gcpc/gcsp to syscallpc/syscallsp.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12250043
»»»
R=rsc
CC=golang-dev
https://golang.org/cl/12424045
It was needed for the old scheduler,
because there temporary could be more threads than gomaxprocs.
In the new scheduler gomaxprocs is always respected.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12438043
gcpc/gcsp are used by GC in similar situation.
gcpc/gcsp are also more stable than gp->sched,
because gp->sched is mutated by entersyscall/exitsyscall
in morestack and mcall. So it has higher chances of being inconsistent.
Also, rename gcpc/gcsp to syscallpc/syscallsp.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/12250043
Make it accept type, combine flags.
Several reasons for the change:
1. mallocgc and settype must be atomic wrt GC
2. settype is called from only one place now
3. it will help performance (eventually settype
functionality must be combined with markallocated)
4. flags are easier to read now (no mallocgc(sz, 0, 1, 0) anymore)
R=golang-dev, iant, nightlyone, rsc, dave, khr, bradfitz, r
CC=golang-dev
https://golang.org/cl/10136043
This CL introduces a FUNCDATA number for runtime-specific
garbage collection metadata, changes the C and Go compilers
to emit that metadata, and changes the runtime to expect it.
The old pseudo-instructions that carried this information
are gone, as is the linker code to process them.
R=golang-dev, dvyukov, cshapiro
CC=golang-dev
https://golang.org/cl/11406044