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Date: Sun, 26 May 2013 13:50:53 -0700
From: Davidlohr Bueso <davidlohr.bueso@...com>
To: Manfred Spraul <manfred@...orfullife.com>
Cc: Rik van Riel <riel@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>, hhuang@...hat.com,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/4] ipc/sem.c: Bug fixes, regression fixes, v3
On Sun, 2013-05-26 at 11:08 +0200, Manfred Spraul wrote:
> I've split my patch into 4 parts:
> - 1: Fix-missing-wakeups-in-do_smart_update
> - 2: seperate-wait-for-zero-and-alter-tasks
> - 3: Always-use-only-one-queue-for-alter-operations
> - 4: Rename-try_atomic_semop-to-perform_atomic
>
> Linus:
> - Patch 1 should be merged immediately: It fixes bugs,
> the current code misses wakeups.
Nothing against this.
> - Patch 2 and 3 restore the behavior of linux <=3.0.9.
> I would propose that they are merged, too: I can't rule out that
> changing the priority of the wakeups breaks user space apps.
>
> - Patch 4 is trivial, no code changes at all.
> If 2+3 are merged, then 4 should be merged, too.
>
> I have tested patch 1 seperately and 1+2+3+4:
> With patch 1 applied, there are no more missed wakeups.
>
> With all 4 applied, linux-3.0.10-rc1 behaves as linux <=3.0.9.
>
> With regards to the scalability, I do not expect any degradation:
> Operations on seperate semaphores in an array remain parallelized.
In lack of getting my swingbench DSS environment back, I ran these
changes against the semop-multi program on my laptop. For 256 threads,
with Manfred's patchset the ops/sec suffers around -7.3%.
3.10-rc2-baseline:
cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
total operations: 325289276, ops/sec 10842975
- 18.14% a.out [kernel.kallsyms] [k] SYSC_semtimedop ◆
- SYSC_semtimedop ▒
+ 97.54% SyS_semtimedop ▒
+ 2.46% SyS_semop
- 5.24% a.out [kernel.kallsyms] [k] ipc_obtain_object_check ▒
- ipc_obtain_object_check ▒
+ 92.37% SYSC_semtimedop ▒
+ 7.63% SyS_semtimedop
- 4.67% a.out [kernel.kallsyms] [k] _raw_spin_lock ▒
- _raw_spin_lock ▒
+ 91.98% SYSC_semtimedop ▒
+ 7.89% SyS_semtimedop
3.10-rc2-manfred:
cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
total operations: 303314830, ops/sec 10110494
- 17.10% a.out [kernel.kallsyms] [k] SYSC_semtimedop ◆
- SYSC_semtimedop ▒
+ 97.47% SyS_semtimedop ▒
+ 2.53% SyS_semop
- 4.79% a.out [kernel.kallsyms] [k] ipc_obtain_object_check ▒
- ipc_obtain_object_check ▒
+ 91.88% SYSC_semtimedop ▒
+ 8.12% SyS_semtimedop
- 4.50% a.out [kernel.kallsyms] [k] _raw_spin_lock ▒
- _raw_spin_lock ▒
+ 90.92% SYSC_semtimedop ▒
+ 8.95% SyS_semtimedop
3.9:
cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
total operations: 151293714, ops/sec 5043123
- 59.73% a.out [kernel.kallsyms] [k] _raw_spin_lock ◆
- _raw_spin_lock ▒
+ 98.86% ipc_lock ▒
+ 1.13% ipc_lock_check ▒
- 6.48% a.out [kernel.kallsyms] [k] sys_semtimedop ▒
- sys_semtimedop ▒
+ 95.26% sys_semop ▒
+ 4.74% system_call_fastpath
While I'm not happy about the [smallish] throughput impact, I'm not as
against this patchset as I was originally. I still think that such
changes, if applied, should go through the linux-next/3.11 phase as much
testing is still needed. I'd also like to see how the Oracle benchmark
behaves (yes, it should be more or less faithful to how semop-multi is
impacted).
Thanks,
Davidlohr
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