From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Airlie <airlied@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dri-devel@lists.sf.net, Tomi Valkeinen <tomi.valkeinen@ti.com>
Subject: Re: [PATCH] vt_buffer: drop console buffer copying optimisations
Date: Thu, 29 Jan 2015 15:57:42 -0800 [thread overview]
Message-ID: <20150129235742.GB14741@kroah.com> (raw)
In-Reply-To: <CA+55aFw75+RrQ7QfrTvsOAc0cKRuNASA9OUqwuwpA7n=QTTe5w@mail.gmail.com>
On Thu, Jan 29, 2015 at 03:40:33PM -0800, Linus Torvalds wrote:
> On Wed, Jan 28, 2015 at 8:11 PM, Dave Airlie <airlied@redhat.com> wrote:
> >
> > Linus, this came up a while back I finally got some confirmation
> > that it fixes those servers.
>
> I'm certainly ok with this. which way should it go in? The users are:
>
> - drivers/tty/vt/vt.c (Greg KH, "tty layer")
>
> - drivers/video/console/* (fbcon people: Tomi Valkeinen and friends)
>
> and it might make sense to have *some* indication of how much worse
> this makes fbcon performance in particular..
>
> Greg/Tomi - the patch is removing this:
>
> #define scr_memcpyw(d, s, c) memcpy(d, s, c)
> #define scr_memmovew(d, s, c) memmove(d, s, c)
> #define VT_BUF_HAVE_MEMCPYW
> #define VT_BUF_HAVE_MEMMOVEW
>
> from <linux/vt_buffer.h>, because some stupid graphics cards
> apparently cannot handle 64-bit accesses of regular memcpy/memmove.
>
> And on other setups, this will be the reverse: 8-bit accesses due to
> using "rep movsb", which is the fast way to move/clear memory on
> modern Intel CPU's, but is really wrong for MMIO where it will be slow
> as hell.
>
> So just getting rid of the memcpy/memmove is likely the right thing in
> general, since the fallbacks go this the traditional 16-bit-at-a-time
> way. And getting rid of the memcpy _may_ speed things up.
>
> But if it slows things down, we might have to try something else. Like
> saying "all cards we've ever seen have been ok with aligned 32-bit
> accesses", and extend the open-coded scr_memcpy/memmove functions to
> do that.
>
> Hmm?
I can take this through the tty tree, but can I put it in linux-next and
wait for the 3.20 merge window to give people who might notice a
slow-down a chance to object?
thanks,
greg k-h
next prev parent reply other threads:[~2015-01-29 23:57 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-29 4:11 [PATCH] vt_buffer: drop console buffer copying optimisations Dave Airlie
2015-01-29 12:06 ` Peter Hurley
2015-01-29 23:40 ` Linus Torvalds
2015-01-29 23:57 ` Greg Kroah-Hartman [this message]
2015-01-30 0:03 ` Linus Torvalds
2015-01-30 0:14 ` Dave Airlie
2015-02-03 15:54 ` One Thousand Gnomes
2015-02-05 9:01 ` Geert Uytterhoeven
2015-02-05 11:35 ` One Thousand Gnomes
2015-02-09 10:35 ` Daniel Stone
2015-02-09 10:49 ` Geert Uytterhoeven
2015-02-09 11:00 ` Daniel Stone
2015-02-09 20:17 ` One Thousand Gnomes
2015-02-24 16:49 ` Pavel Machek
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