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From: Dave Chinner <david@fromorbit.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Minchan Kim <minchan@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Hugh Dickins <hughd@google.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K
Date: Tue, 3 Jun 2014 08:59:11 +1000	[thread overview]
Message-ID: <20140602225911.GU14410@dastard> (raw)
In-Reply-To: <5389393D.2030305@kernel.dk>

On Fri, May 30, 2014 at 08:06:53PM -0600, Jens Axboe wrote:
> On 2014-05-28 20:42, Linus Torvalds wrote:
> >Well, we've definitely have had some issues with deeper callchains
> >with md, but I suspect virtio might be worse, and the new blk-mq code
> >is lilkely worse in this respect too.
> 
> I don't think blk-mq is worse than the older stack, in fact it
> should be better. The call chains are shorter, and a lot less cruft
> on the stack. Historically the stack issues have been nested
> devices, however. And for sync IO, we do run it inline, so if the
> driver chews up a lot of stack, well...

Hi Jens - as we found out with the mm code, there's a significant
disconnect between what the code looks like (i.e. it may use very
little stack directly) and what the compiler is generating.

Before blk-mq:

  9)     3952     112   scsi_request_fn+0x4b/0x490
 10)     3840      32   __blk_run_queue+0x37/0x50
 11)     3808      64   queue_unplugged+0x39/0xb0
 12)     3744     112   blk_flush_plug_list+0x20b/0x240

Now with blk-mq:

  3)     4672      96   virtio_queue_rq+0xd2/0x1e0
  4)     4576     128   __blk_mq_run_hw_queue+0x1f0/0x3e0
  5)     4448      16   blk_mq_run_hw_queue+0x35/0x40
  6)     4432      80   blk_mq_insert_requests+0xc7/0x130
  7)     4352      96   blk_mq_flush_plug_list+0x129/0x140
  8)     4256     112   blk_flush_plug_list+0xe7/0x230

So previously flushing a plug used rough 200 bytes of stack.  With
blk-mq, it's over 400 bytes. IOWs, blk-mq has more than doubled the
block layer stack usage...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  reply	other threads:[~2014-06-02 22:59 UTC|newest]

Thread overview: 107+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-28  6:53 [PATCH 1/2] ftrace: print stack usage right before Oops Minchan Kim
2014-05-28  6:53 ` [RFC 2/2] x86_64: expand kernel stack to 16K Minchan Kim
2014-05-28  8:37   ` Dave Chinner
2014-05-28  9:13     ` Dave Chinner
2014-05-28 16:06       ` Johannes Weiner
2014-05-28 21:55         ` Dave Chinner
2014-05-29  6:06         ` Minchan Kim
2014-05-28  9:04   ` Michael S. Tsirkin
2014-05-29  1:09     ` Minchan Kim
2014-05-29  2:44       ` Steven Rostedt
2014-05-29  4:11         ` Minchan Kim
2014-05-29  2:47       ` Rusty Russell
2014-05-29  4:10     ` virtio_ring stack usage Rusty Russell
2014-05-28  9:27   ` [RFC 2/2] x86_64: expand kernel stack to 16K Borislav Petkov
2014-05-29 13:23     ` One Thousand Gnomes
2014-05-28 14:14   ` Steven Rostedt
2014-05-28 14:23     ` H. Peter Anvin
2014-05-28 22:11       ` Dave Chinner
2014-05-28 22:42         ` H. Peter Anvin
2014-05-28 23:17           ` Dave Chinner
2014-05-28 23:21             ` H. Peter Anvin
2014-05-28 15:43   ` Richard Weinberger
2014-05-28 16:08     ` Steven Rostedt
2014-05-28 16:11       ` Richard Weinberger
2014-05-28 16:13       ` Linus Torvalds
2014-05-28 16:09   ` Linus Torvalds
2014-05-28 22:31     ` Dave Chinner
2014-05-28 22:41       ` Linus Torvalds
2014-05-29  1:30         ` Dave Chinner
2014-05-29  1:58           ` Dave Chinner
2014-05-29  2:51             ` Linus Torvalds
2014-05-29 23:36             ` Minchan Kim
2014-05-30  0:05               ` Linus Torvalds
2014-05-30  0:20                 ` Minchan Kim
2014-05-30  0:31                   ` Linus Torvalds
2014-05-30  0:50                     ` Minchan Kim
2014-05-30  1:24                       ` Linus Torvalds
2014-05-30  1:58                         ` Dave Chinner
2014-05-30  2:13                           ` Linus Torvalds
2014-05-30  6:21                         ` Minchan Kim
2014-05-30  1:30                 ` Linus Torvalds
2014-05-30  0:15               ` Dave Chinner
2014-05-30  2:12                 ` Minchan Kim
2014-05-30  4:37                   ` Linus Torvalds
2014-05-31  1:45                     ` Linus Torvalds
2014-05-30  6:12                   ` Minchan Kim
2014-06-03 13:28                   ` Rasmus Villemoes
2014-06-03 19:04                     ` Linus Torvalds
2014-06-10 12:29                       ` [PATCH 0/2] Per-task wait_queue_t Rasmus Villemoes
2014-06-10 12:29                         ` [PATCH 1/2] wait: Introduce per-task wait_queue_t Rasmus Villemoes
2014-06-11 15:16                           ` Oleg Nesterov
2014-06-10 12:29                         ` [PATCH 2/2] wait: Use the per-task wait_queue_t in ___wait_event macro Rasmus Villemoes
2014-06-10 15:50                         ` [PATCH 0/2] Per-task wait_queue_t Peter Zijlstra
2014-06-12 21:46                           ` Rasmus Villemoes
2014-05-29  2:42           ` [RFC 2/2] x86_64: expand kernel stack to 16K Linus Torvalds
2014-05-29  5:14             ` H. Peter Anvin
2014-05-29  6:01             ` Rusty Russell
2014-05-29  7:26               ` virtio ring cleanups, which save stack on older gcc Rusty Russell
2014-05-29  7:26                 ` [PATCH 1/4] Hack: measure stack taken by vring from virtio_blk Rusty Russell
2014-05-29 15:39                   ` Linus Torvalds
2014-05-29  7:26                 ` [PATCH 2/4] virtio_net: pass well-formed sg to virtqueue_add_inbuf() Rusty Russell
2014-05-29 10:07                   ` Michael S. Tsirkin
2014-05-29  7:26                 ` [PATCH 3/4] virtio_ring: assume sgs are always well-formed Rusty Russell
2014-05-29 11:18                   ` Michael S. Tsirkin
2014-05-29  7:26                 ` [PATCH 4/4] virtio_ring: unify direct/indirect code paths Rusty Russell
2014-05-29  7:52                   ` Peter Zijlstra
2014-05-29 11:05                     ` Rusty Russell
2014-05-29 11:33                       ` Michael S. Tsirkin
2014-05-29 11:29                   ` Michael S. Tsirkin
2014-05-30  2:37                     ` Rusty Russell
2014-05-30  6:21                       ` Rusty Russell
2014-05-29  7:41                 ` virtio ring cleanups, which save stack on older gcc Minchan Kim
2014-05-29 10:39                   ` Dave Chinner
2014-05-29 11:08                   ` Rusty Russell
2014-05-29 23:45                     ` Minchan Kim
2014-05-30  1:06                       ` Minchan Kim
2014-05-30  6:56                       ` Rusty Russell
2014-05-29  7:26             ` [RFC 2/2] x86_64: expand kernel stack to 16K Dave Chinner
2014-05-29 15:24               ` Linus Torvalds
2014-05-29 23:40                 ` Minchan Kim
2014-05-29 23:53                 ` Dave Chinner
2014-05-30  0:06                   ` Dave Jones
2014-05-30  0:21                     ` Dave Chinner
2014-05-30  0:29                       ` Dave Jones
2014-05-30  0:32                       ` Minchan Kim
2014-05-30  1:34                         ` Dave Chinner
2014-05-30 15:25                           ` H. Peter Anvin
2014-05-30 15:41                             ` Linus Torvalds
2014-05-30 15:52                               ` H. Peter Anvin
2014-05-30 16:06                                 ` Linus Torvalds
2014-05-30 17:24                                   ` Dave Hansen
2014-05-30 18:12                                     ` H. Peter Anvin
2014-10-21  2:00                               ` Dave Jones
2014-10-21  4:59                                 ` Andy Lutomirski
2014-05-30  9:48                 ` Richard Weinberger
2014-05-30 15:36                   ` Linus Torvalds
2014-05-31  2:06             ` Jens Axboe
2014-06-02 22:59               ` Dave Chinner [this message]
2014-06-03 13:02               ` Konstantin Khlebnikov
2014-05-29  3:46     ` Minchan Kim
2014-05-29  4:13       ` Linus Torvalds
2014-05-29  5:10         ` Minchan Kim
2014-05-30 21:23     ` Andi Kleen
2014-05-28 16:18 ` [PATCH 1/2] ftrace: print stack usage right before Oops Steven Rostedt
2014-05-29  3:52   ` Minchan Kim
2014-05-29  3:01 ` Steven Rostedt
2014-05-29  3:49   ` Minchan Kim

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