From: Jens Axboe <axboe@kernel.dk>
To: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <koverstreet@google.com>,
linux-kernel@vger.kernel.org, linux-aio@kvack.org,
linux-fsdevel@vger.kernel.org, zab@redhat.com, bcrl@kvack.org,
jmoyer@redhat.com, viro@zeniv.linux.org.uk, tytso@mit.edu,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 23/32] Generic dynamic per cpu refcounting
Date: Fri, 8 Feb 2013 15:49:02 +0100 [thread overview]
Message-ID: <20130208144902.GQ15092@kernel.dk> (raw)
In-Reply-To: <20130208144408.GY2875@htj.dyndns.org>
On Fri, Feb 08 2013, Tejun Heo wrote:
> (cc'ing Andrew)
>
> On Wed, Dec 26, 2012 at 06:00:02PM -0800, Kent Overstreet wrote:
> > This implements a refcount with similar semantics to
> > atomic_get()/atomic_dec_and_test(), that starts out as just an atomic_t
> > but dynamically switches to per cpu refcounting when the rate of
> > gets/puts becomes too high.
> >
> > It also implements two stage shutdown, as we need it to tear down the
> > percpu counts. Before dropping the initial refcount, you must call
> > percpu_ref_kill(); this puts the refcount in "shutting down mode" and
> > switches back to a single atomic refcount with the appropriate barriers
> > (synchronize_rcu()).
> >
> > It's also legal to call percpu_ref_kill() multiple times - it only
> > returns true once, so callers don't have to reimplement shutdown
> > synchronization.
> >
> > For the sake of simplicity/efficiency, the heuristic is pretty simple -
> > it just switches to percpu refcounting if there are more than x gets
> > in one second (completely arbitrarily, 4096).
> >
> > It'd be more correct to count the number of cache misses or something
> > else more profile driven, but doing so would require accessing the
> > shared ref twice per get - by just counting the number of gets(), we can
> > stick that counter in the high bits of the refcount and increment both
> > with a single atomic64_add(). But I expect this'll be good enough in
> > practice.
> >
> > Signed-off-by: Kent Overstreet <koverstreet@google.com>
>
> What's the status of this series? The percpu-refcnt part is still
> going through review and the merge window is opening up pretty soon.
> Kent, Andrew?
I'd feel a lot better deferring the whole aio/dio performance series for
one merge window. There's very little point in rushing it, and I don't
think it's been reviewed/tested enough yet.
--
Jens Axboe
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next prev parent reply other threads:[~2013-02-08 14:49 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-27 1:59 [PATCH 00/32] AIO performance improvements/cleanups, v3 Kent Overstreet
2012-12-27 1:59 ` [PATCH 01/32] mm: remove old aio use_mm() comment Kent Overstreet
2012-12-27 1:59 ` [PATCH 02/32] aio: remove dead code from aio.h Kent Overstreet
2012-12-27 1:59 ` [PATCH 03/32] gadget: remove only user of aio retry Kent Overstreet
2012-12-27 1:59 ` [PATCH 04/32] aio: remove retry-based AIO Kent Overstreet
2012-12-29 7:36 ` Hillf Danton
2013-01-07 22:12 ` Kent Overstreet
2012-12-29 7:47 ` Hillf Danton
2013-01-07 22:15 ` Kent Overstreet
2012-12-27 1:59 ` [PATCH 05/32] char: add aio_{read,write} to /dev/{null,zero} Kent Overstreet
2012-12-27 1:59 ` [PATCH 06/32] aio: Kill return value of aio_complete() Kent Overstreet
2012-12-27 1:59 ` [PATCH 07/32] aio: kiocb_cancel() Kent Overstreet
2012-12-27 1:59 ` [PATCH 08/32] aio: Move private stuff out of aio.h Kent Overstreet
2012-12-27 1:59 ` [PATCH 09/32] aio: dprintk() -> pr_debug() Kent Overstreet
2012-12-27 1:59 ` [PATCH 10/32] aio: do fget() after aio_get_req() Kent Overstreet
2012-12-27 1:59 ` [PATCH 11/32] aio: Make aio_put_req() lockless Kent Overstreet
2012-12-27 1:59 ` [PATCH 12/32] aio: Refcounting cleanup Kent Overstreet
2012-12-27 1:59 ` [PATCH 13/32] wait: Add wait_event_hrtimeout() Kent Overstreet
2012-12-27 10:37 ` Fubo Chen
2013-01-03 23:08 ` Andrew Morton
2013-01-08 0:09 ` Kent Overstreet
2012-12-27 1:59 ` [PATCH 14/32] aio: Make aio_read_evt() more efficient, convert to hrtimers Kent Overstreet
2013-01-03 23:19 ` Andrew Morton
2013-01-08 0:28 ` Kent Overstreet
2013-01-08 1:00 ` Andrew Morton
2013-01-08 1:28 ` Kent Overstreet
2012-12-27 1:59 ` [PATCH 15/32] aio: Use flush_dcache_page() Kent Overstreet
2012-12-27 1:59 ` [PATCH 16/32] aio: Use cancellation list lazily Kent Overstreet
2012-12-27 1:59 ` [PATCH 17/32] aio: Change reqs_active to include unreaped completions Kent Overstreet
2012-12-27 1:59 ` [PATCH 18/32] aio: Kill batch allocation Kent Overstreet
2012-12-27 1:59 ` [PATCH 19/32] aio: Kill struct aio_ring_info Kent Overstreet
2012-12-27 1:59 ` [PATCH 20/32] aio: Give shared kioctx fields their own cachelines Kent Overstreet
2013-01-03 23:25 ` Andrew Morton
2013-01-07 23:48 ` Kent Overstreet
2012-12-27 2:00 ` [PATCH 21/32] aio: reqs_active -> reqs_available Kent Overstreet
2012-12-27 2:00 ` [PATCH 22/32] aio: percpu reqs_available Kent Overstreet
2012-12-27 2:00 ` [PATCH 23/32] Generic dynamic per cpu refcounting Kent Overstreet
2013-01-03 22:48 ` Andrew Morton
2013-01-07 23:47 ` Kent Overstreet
2013-01-08 1:03 ` [PATCH] percpu-refcount: Sparse fixes Kent Overstreet
2013-01-25 0:51 ` [PATCH 23/32] Generic dynamic per cpu refcounting Tejun Heo
2013-01-25 1:13 ` Kent Overstreet
2013-01-25 2:03 ` Tejun Heo
2013-01-25 2:09 ` Tejun Heo
2013-01-28 17:48 ` Kent Overstreet
2013-01-28 18:18 ` Tejun Heo
2013-01-25 6:15 ` Rusty Russell
2013-01-28 17:53 ` Kent Overstreet
2013-01-28 17:59 ` Tejun Heo
2013-01-28 18:32 ` Kent Overstreet
2013-01-28 18:57 ` Christoph Lameter
2013-02-08 14:44 ` Tejun Heo
2013-02-08 14:49 ` Jens Axboe [this message]
2013-02-08 17:50 ` Andrew Morton
2013-02-08 21:27 ` Kent Overstreet
2013-02-11 14:21 ` Jeff Moyer
2013-02-08 21:17 ` Kent Overstreet
2012-12-27 2:00 ` [PATCH 24/32] aio: Percpu ioctx refcount Kent Overstreet
2012-12-27 2:00 ` [PATCH 25/32] aio: use xchg() instead of completion_lock Kent Overstreet
2013-01-03 23:34 ` Andrew Morton
2013-01-07 23:21 ` Kent Overstreet
2013-01-07 23:35 ` Andrew Morton
2013-01-08 0:01 ` Kent Overstreet
2012-12-27 2:00 ` [PATCH 26/32] aio: Don't include aio.h in sched.h Kent Overstreet
2012-12-27 2:00 ` [PATCH 27/32] aio: Kill ki_key Kent Overstreet
2012-12-27 2:00 ` [PATCH 28/32] aio: Kill ki_retry Kent Overstreet
2012-12-27 2:00 ` [PATCH 29/32] block, aio: Batch completion for bios/kiocbs Kent Overstreet
2013-01-04 9:22 ` Jens Axboe
2013-01-07 23:34 ` Kent Overstreet
2013-01-08 15:33 ` Jeff Moyer
2013-01-08 16:06 ` Kent Overstreet
2013-01-08 16:15 ` Jeff Moyer
2013-01-08 16:48 ` Kent Overstreet
2012-12-27 2:00 ` [PATCH 30/32] virtio-blk: Convert to batch completion Kent Overstreet
2012-12-27 2:00 ` [PATCH 31/32] mtip32xx: " Kent Overstreet
2012-12-27 2:00 ` [PATCH 32/32] aio: Smoosh struct kiocb Kent Overstreet
2013-01-04 9:22 ` [PATCH 00/32] AIO performance improvements/cleanups, v3 Jens Axboe
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