From: Kent Overstreet <koverstreet@google.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>,
linux-kernel@vger.kernel.org, linux-aio@kvack.org,
linux-fsdevel@vger.kernel.org, zab@redhat.com, jmoyer@redhat.com,
axboe@kernel.dk, viro@zeniv.linux.org.uk
Subject: Re: [PATCH 22/25] Generic dynamic per cpu refcounting
Date: Thu, 29 Nov 2012 12:59:20 -0800 [thread overview]
Message-ID: <20121129205920.GL15094@google.com> (raw)
In-Reply-To: <20121129205447.GY16230@one.firstfloor.org>
On Thu, Nov 29, 2012 at 09:54:47PM +0100, Andi Kleen wrote:
> > > The regular atomic_t is limited in ways that you are not.
> > > See my original mail.
> >
> > I don't follow, can you explain?
>
> For most cases the reference count is tied to some object, which are
> naturally limited by memory size or other physical resources.
>
> But in the assymetric CPU case with your ref count no such limiter
> exists.
It's got exactly the same limit as the old code which used the atomic_t
- we're limited by the number of threads that can be issuing aio
syscalls at a time.
The assymetry you're talking about _doesn't matter_, individual cpu
counters wrapping does not affect what the counters all sum to when we
go to tear down.
A coworker at lunch actually pointed out to me that the reason this is
true is just that modular arithmatic is still associative with addition
and subtraction.
next prev parent reply other threads:[~2012-11-29 20:59 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-28 16:43 [PATCH 00/25] AIO performance improvements/cleanups Kent Overstreet
2012-11-28 16:43 ` [PATCH 01/25] mm: remove old aio use_mm() comment Kent Overstreet
2012-11-28 16:43 ` [PATCH 02/25] aio: remove dead code from aio.h Kent Overstreet
2012-11-28 16:43 ` [PATCH 03/25] gadget: remove only user of aio retry Kent Overstreet
2012-11-28 16:43 ` [PATCH 04/25] aio: remove retry-based AIO Kent Overstreet
2012-11-28 16:43 ` [PATCH 05/25] char: add aio_{read,write} to /dev/{null,zero} Kent Overstreet
2012-11-28 16:43 ` [PATCH 06/25] aio: Kill return value of aio_complete() Kent Overstreet
2012-11-28 16:43 ` [PATCH 07/25] aio: kiocb_cancel() Kent Overstreet
2012-11-29 0:07 ` Zach Brown
2012-11-29 0:58 ` Kent Overstreet
2012-11-28 16:43 ` [PATCH 08/25] aio: Move private stuff out of aio.h Kent Overstreet
2012-11-28 16:43 ` [PATCH 09/25] aio: dprintk() -> pr_debug() Kent Overstreet
2012-11-28 16:43 ` [PATCH 10/25] aio: do fget() after aio_get_req() Kent Overstreet
2012-11-28 16:43 ` [PATCH 11/25] aio: Make aio_put_req() lockless Kent Overstreet
2012-11-28 16:43 ` [PATCH 12/25] aio: Refcounting cleanup Kent Overstreet
2012-11-29 0:17 ` Zach Brown
2012-11-29 1:12 ` Kent Overstreet
2012-11-29 0:46 ` Benjamin LaHaise
2012-11-29 1:38 ` Kent Overstreet
2012-11-28 16:43 ` [PATCH 13/25] aio: Convert read_events() to hrtimers Kent Overstreet
2012-11-29 0:24 ` Zach Brown
2012-11-29 1:05 ` Kent Overstreet
2012-11-28 16:43 ` [PATCH 14/25] aio: Make aio_read_evt() more efficient Kent Overstreet
2012-11-29 0:38 ` Zach Brown
2012-11-29 19:31 ` Kent Overstreet
2012-11-30 0:20 ` Kent Overstreet
2012-11-28 16:43 ` [PATCH 15/25] aio: Use cancellation list lazily Kent Overstreet
2012-11-28 16:43 ` [PATCH 16/25] aio: Change reqs_active to include unreaped completions Kent Overstreet
2012-11-28 16:43 ` [PATCH 17/25] aio: Kill batch allocation Kent Overstreet
2012-11-28 16:43 ` [PATCH 18/25] aio: Kill struct aio_ring_info Kent Overstreet
2012-11-28 16:43 ` [PATCH 19/25] aio: Give shared kioctx fields their own cachelines Kent Overstreet
2012-11-28 16:43 ` [PATCH 20/25] aio: reqs_active -> reqs_available Kent Overstreet
2012-11-28 16:43 ` [PATCH 21/25] aio: percpu reqs_available Kent Overstreet
2012-11-28 16:43 ` [PATCH 22/25] Generic dynamic per cpu refcounting Kent Overstreet
2012-11-29 18:45 ` Andi Kleen
2012-11-29 18:57 ` Kent Overstreet
2012-11-29 18:59 ` Andi Kleen
2012-11-29 19:12 ` Kent Overstreet
2012-11-29 19:20 ` Andi Kleen
2012-11-29 19:29 ` Kent Overstreet
2012-11-29 19:34 ` Benjamin LaHaise
2012-11-29 20:22 ` Kent Overstreet
2012-11-29 20:42 ` Andi Kleen
2012-11-29 20:45 ` Kent Overstreet
2012-11-29 20:54 ` Andi Kleen
2012-11-29 20:59 ` Kent Overstreet [this message]
2012-11-29 21:57 ` Jamie Lokier
2012-11-28 16:43 ` [PATCH 23/25] aio: Percpu ioctx refcount Kent Overstreet
2012-11-28 16:43 ` [PATCH 24/25] aio: use xchg() instead of completion_lock Kent Overstreet
2012-11-28 16:43 ` [PATCH 25/25] aio: Don't include aio.h in sched.h Kent Overstreet
2012-11-29 0:03 ` [PATCH 00/25] AIO performance improvements/cleanups Zach Brown
2012-11-29 19:01 ` Kent Overstreet
-- strict thread matches above, loose matches on Subject: below --
2012-11-28 3:19 Kent Overstreet
2012-11-28 3:19 ` [PATCH 22/25] Generic dynamic per cpu refcounting Kent Overstreet
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