From: Al Viro <viro@zeniv.linux.org.uk>
To: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>,
Matthew Wilcox <willy@infradead.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC] what to do with IOCB_DSYNC?
Date: Mon, 23 May 2022 16:15:13 +0000 [thread overview]
Message-ID: <YouzEUI5kBTq46C6@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <6594c360-0c7c-412f-29c9-377ddda16937@kernel.dk>
On Mon, May 23, 2022 at 09:12:32AM -0600, Jens Axboe wrote:
> > There's several more, AFAICS (cifs, ceph, fuse, gfs2)... The check in
> > /dev/fuse turned out to be fine - it's only using primitives, so we
> > can pass ITER_UBUF ones there. mm/shmem.c check... similar, but I
> > really wonder if x86 clear_user() really sucks worse than
> > copy_to_user() from zero page...
>
> Yep, not surprised if it isn't complete, I just tackled the ones I
> found. I do like the idea of having a generic check for that rather
> than implicit knowledge about which iter types may contain user memory.
>
> I haven't looked at clear_user() vs copy_to_user() from the zero page.
> But should be trivial to benchmark and profile. I'll try and do that
> when I find some time.
FWIW, having looked at __clear_user() in arch/x86/lib/usercopy_64.c...
I'm not at all surprised. It should be parallel to memset_64.S;
as it is, we have
loop with one 64bit store per iteration + loop with 8bit stores
for the tail, with no attempts to align anything
vs.
rep stosb if CPU has optimized rep stosb; otherwise
rep stosq + rep stosb on CPUs that don't suck at rep sto* in general;
otherwise align, then do loop with 8*64bit stores, then loop with
64bit stores, then loop with 8bit stores
Shouldn't be hard to do uaccess parallel for that. Reads from /dev/zero,
if nothing else, would benefit...
Might be worth doing what sparc does, with shared asm for both - it's
an out-of-line code anyway, with most of the payload trivially shared...
next prev parent reply other threads:[~2022-05-23 16:15 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-21 0:46 [RFC] what to do with IOCB_DSYNC? Al Viro
2021-06-21 13:59 ` Christoph Hellwig
2021-06-21 14:03 ` Matthew Wilcox
2021-06-21 14:09 ` Christoph Hellwig
2021-06-21 14:16 ` Matthew Wilcox
2021-06-21 14:22 ` Christoph Hellwig
2021-06-21 14:32 ` Al Viro
2021-06-21 14:35 ` Christoph Hellwig
2021-06-21 15:22 ` Jens Axboe
2022-05-21 17:48 ` Al Viro
2022-05-21 19:03 ` Jens Axboe
2022-05-21 22:14 ` Jens Axboe
2022-05-22 7:45 ` Christoph Hellwig
2022-05-22 10:23 ` Matthew Wilcox
2022-05-22 10:36 ` Al Viro
2022-05-22 11:15 ` Matthew Wilcox
2022-05-22 11:45 ` Christoph Hellwig
2022-05-22 12:39 ` Jens Axboe
2022-05-22 12:48 ` Al Viro
2022-05-22 13:02 ` Jens Axboe
2022-05-22 13:07 ` Al Viro
2022-05-22 13:09 ` Jens Axboe
2022-05-22 18:06 ` Jens Axboe
2022-05-22 18:25 ` Al Viro
2022-05-22 18:29 ` Jens Axboe
2022-05-22 18:39 ` Al Viro
2022-05-22 18:48 ` Jens Axboe
2022-05-22 19:04 ` Al Viro
2022-05-22 20:03 ` Jens Axboe
2022-05-23 0:42 ` Al Viro
2022-05-23 1:22 ` Jens Axboe
2022-05-23 1:28 ` Jens Axboe
2022-05-23 1:50 ` Jens Axboe
2022-05-23 2:43 ` Jens Axboe
2022-05-23 14:22 ` Al Viro
2022-05-23 14:34 ` Jens Axboe
2022-05-23 14:47 ` Al Viro
2022-05-23 15:12 ` Jens Axboe
2022-05-23 15:44 ` Jens Axboe
2022-05-23 15:49 ` Matthew Wilcox
2022-05-23 15:55 ` Jens Axboe
2022-05-23 16:03 ` Jens Axboe
2022-05-26 14:46 ` Jason A. Donenfeld
2022-05-27 10:09 ` Ingo Molnar
2022-05-27 10:15 ` Jason A. Donenfeld
2022-05-27 14:45 ` Samuel Neves
2022-05-27 10:25 ` Ingo Molnar
2022-05-27 10:36 ` Borislav Petkov
2022-05-28 20:54 ` Sedat Dilek
2022-05-28 20:38 ` Sedat Dilek
2022-05-28 20:39 ` Sedat Dilek
2022-05-23 16:15 ` Al Viro [this message]
2022-05-25 14:34 ` Matthew Wilcox
2022-05-26 23:19 ` Al Viro
2022-05-27 14:51 ` Jens Axboe
2022-05-22 12:21 ` Al Viro
2022-05-22 7:43 ` Christoph Hellwig
2022-05-22 12:41 ` Al Viro
2022-05-22 12:51 ` Christoph Hellwig
2021-06-21 14:22 ` Al Viro
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