From: Manfred Spraul <manfred@colorfullife.com>
To: Chris Mason <chris.mason@oracle.com>,
Nick Piggin <npiggin@suse.de>,
zach.brown@oracle.com, jens.axboe@oracle.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] ipc semaphores: reduce ipc_lock contention in semtimedop
Date: Wed, 14 Apr 2010 18:16:53 +0200 [thread overview]
Message-ID: <4BC5EA75.9090803@colorfullife.com> (raw)
In-Reply-To: <20100413181937.GM13327@think>
On 04/13/2010 08:19 PM, Chris Mason wrote:
> On Wed, Apr 14, 2010 at 04:09:45AM +1000, Nick Piggin wrote:
>
>> On Tue, Apr 13, 2010 at 01:39:41PM -0400, Chris Mason wrote:
>>
>> The other thing I don't know if your patch gets right is requeueing on
>> of the operations. When you requeue from one list to another, then you
>> seem to lose ordering with other pending operations, so that would
>> seem to break the API as well (can't remember if the API strictly
>> mandates FIFO, but anyway it can open up starvation cases).
>>
> I don't see anything in the docs about the FIFO order. I could add an
> extra sort on sequence number pretty easily, but is the starvation case
> really that bad?
>
>
How do you want to determine the sequence number?
Is atomic_inc_return() on a per-semaphore array counter sufficiently fast?
>> I was looking at doing a sequence number to be able to sort these, but
>> it ended up getting over complex (and SAP was only using simple ops so
>> it didn't seem to need much better).
>>
>> We want to be careful not to change semantics at all. And it gets
>> tricky quickly :( What about Zach's simpler wakeup API?
>>
> Yeah, that's why my patches include code to handle userland sending
> duplicate semids. Zach's simpler API is cooking too, but if I can get
> this done without insane complexity it helps with more than just the
> post/wait oracle workload.
>
>
What is the oracle workload, which multi-sembuf operations does it use?
How many semaphores are in one array?
When the last optimizations were written, I've searched a bit:
- postgres uses per-process semaphores, with small semaphore arrays.
[process sleeps on it's own semaphore and is woken up by someone
else when it can make progress]
- with google, I couldn't find anything relevant that uses multi-sembuf
semop() calls.
And I agree with Nick: We should be careful about changing the API.
--
Manfred
next prev parent reply other threads:[~2010-04-14 16:16 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-12 18:49 [PATCH RFC] Optimize semtimedop Chris Mason
2010-04-12 18:49 ` [PATCH 1/2] ipc semaphores: reduce ipc_lock contention in semtimedop Chris Mason
2010-04-13 17:15 ` Manfred Spraul
2010-04-13 17:39 ` Chris Mason
2010-04-13 18:09 ` Nick Piggin
2010-04-13 18:19 ` Chris Mason
2010-04-13 18:57 ` Nick Piggin
2010-04-13 19:01 ` Chris Mason
2010-04-13 19:25 ` Nick Piggin
2010-04-13 19:38 ` Chris Mason
2010-04-13 20:05 ` Nick Piggin
2010-05-16 16:57 ` Manfred Spraul
2010-05-16 22:40 ` Chris Mason
2010-05-17 7:20 ` Nick Piggin
2010-04-14 16:16 ` Manfred Spraul [this message]
2010-04-14 17:33 ` Chris Mason
2010-04-14 19:11 ` Manfred Spraul
2010-04-14 19:50 ` Chris Mason
2010-04-15 16:33 ` Manfred Spraul
2010-04-15 16:34 ` Chris Mason
2010-04-13 18:24 ` Zach Brown
2010-04-16 11:26 ` Manfred Spraul
2010-04-16 11:45 ` Chris Mason
2010-04-12 18:49 ` [PATCH 2/2] ipc semaphores: order wakeups based on waiter CPU Chris Mason
2010-04-17 10:24 ` Manfred Spraul
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