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

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg
Date	2015-11-30 23:30 +0100
Message-ID	<qAF7k-15b-11@gated-at.bofh.it> (permalink)
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On Mon, Nov 30, 2015 at 02:13:32PM -0500, Waiman Long wrote:
> >This would only work if the structure itself is allocated with cacheline
> >alignment, and looking at sched_create_group(), we use a plain kzalloc()
> >for this, which doesn't guarantee any sort of alignment beyond machine
> >word size IIRC.
> 
> With a RHEL 6 derived .config file, the size of the task_group structure was
> 460 bytes on a 32-bit x86 kernel. Adding a ____cacheline_aligned tag
> increase the size to 512 bytes. So it did make the structure a multiple of
> the cacheline size. With both slub and slab, the allocated task group
> pointers from kzalloc() in sched_create_group() were all multiples of 0x200.
> So they were properly aligned for the ____cacheline_aligned tag to work.

Not sure we should rely on sl*b doing the right thing here.
KMALLOC_MIN_ALIGN is explicitly set to sizeof(long long). If you want
explicit alignment, one should use KMEM_CACHE().
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Thread

[RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg Waiman Long <Waiman.Long@hpe.com> - 2015-11-25 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 11:30 +0100
    Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers  and writers of load_avg Waiman Long <waiman.long@hpe.com> - 2015-11-30 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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