Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync

From	Al Viro <viro@ZenIV.linux.org.uk>
Newsgroups	linux.kernel
Subject	Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync
Date	2016-03-20 02:30 +0100
Message-ID	<reAlP-852-7@gated-at.bofh.it> (permalink)
References	(5 earlier) <qT8Nz-3TE-13@gated-at.bofh.it> <qTYj8-5TC-15@gated-at.bofh.it> <qTYj8-5TC-13@gated-at.bofh.it> <rcEjT-6Ns-11@gated-at.bofh.it> <reAlP-852-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Sat, Mar 19, 2016 at 06:20:24PM -0700, Linus Torvalds wrote:
> On Mon, Mar 14, 2016 at 10:17 AM, Benjamin LaHaise <bcrl@kvack.org> wrote:
> >
> > I had some time last week to make an aio openat do what it can in
> > submit context.  The results are an improvement: when openat is handled
> > in submit context it completes in about half the time it takes compared
> > to the round trip via the work queue, and it's not terribly much code
> > either.
> 
> This looks good to me, and I do suspect that any of these aio paths
> should strive to have a synchronous vs threaded model. I think that
> makes the whole thing much more interesting from a performance
> standpoint.

Umm...  You do realize that LOOKUP_RCU in flags does *NOT* guarantee that
it won't block, right?  At the very least one would need to refuse to
fall back on non-RCU mode without a full restart.  Furthermore, vfs_open()
itself can easily block.

So this new LOOKUP flag makes no sense, and it's in the just about _the_
worst place possible for adding special cases with ill-defined semantics -
do_last() is already far too convoluted and needs untangling, not adding
half-assed kludges.

Thread

Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-20 02:30 +0100
  Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async  fsync Al Viro <viro@ZenIV.linux.org.uk> - 2016-03-20 02:30 +0100
    Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-20 02:50 +0100
      Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async  fsync Al Viro <viro@ZenIV.linux.org.uk> - 2016-03-20 03:00 +0100
        Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-20 03:10 +0100

csiph-web