Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg

From	Waiman Long <waiman.long@hpe.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg
Date	2015-12-02 19:50 +0100
Message-ID	<qBkDw-2x9-11@gated-at.bofh.it> (permalink)
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On 12/01/2015 03:47 AM, Peter Zijlstra wrote:
> On Mon, Nov 30, 2015 at 11:00:35PM -0500, Waiman Long wrote:
>
>> I think the current kernel use power-of-2 kmemcaches to satisfy kalloc()
>> requests except when the size is less than or equal to 192 where there are
>> some non-power-of-2 kmemcaches available. Given that the task_group
>> structure is large enough with FAIR_GROUP_SCHED enabled, we shouldn't hit
>> the case that the allocated buffer is not cacheline aligned.
> Using out-of-object storage is allowed (none of the existing sl*b
> allocators do so iirc).
>
> That is, its perfectly valid for a sl*b allocator for 64 byte objects to
> allocate 72 bytes for each object and use the 'spare' 8 bytes for object
> tracking or whatnot.
>
> That would respect the minimum alignment guarantee of 8 bytes but not
> provide the 'expected' object size alignment you're assuming.
>
> Also, we have the proper interfaces to request the explicit alignment
> for a reason. So if you need the alignment for correctness, use those.

Thanks for the tip. I have just sent out an updated patch set which 
create a cache-aligned memcache for task group. That should work under 
all kernel config setting.

Cheers,
Longman
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Thread

Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Waiman Long <waiman.long@hpe.com> - 2015-11-30 20:20 +0100
  Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Peter Zijlstra <peterz@infradead.org> - 2015-11-30 23:20 +0100
    Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Waiman Long <waiman.long@hpe.com> - 2015-12-01 05:00 +0100
      Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Peter Zijlstra <peterz@infradead.org> - 2015-12-01 09:50 +0100
        Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for  readers and writers of load_avg Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-12-01 11:50 +0100
        Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Waiman Long <waiman.long@hpe.com> - 2015-12-02 19:50 +0100
  Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Peter Zijlstra <peterz@infradead.org> - 2015-11-30 23:30 +0100
    Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Waiman Long <waiman.long@hpe.com> - 2015-12-01 05:10 +0100
      Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Peter Zijlstra <peterz@infradead.org> - 2015-12-01 09:50 +0100
        Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Waiman Long <waiman.long@hpe.com> - 2015-12-02 19:50 +0100
  Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Peter Zijlstra <peterz@infradead.org> - 2015-11-30 23:40 +0100

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