From: Paul Brook <paul@codesourcery.com>
To: qemu-devel@nongnu.org
Cc: Blue Swirl <blauwirbel@gmail.com>
Subject: Re: [Qemu-devel] [6391] Fix nographic mode and VNC
Date: Sun, 25 Jan 2009 23:25:58 +0000 [thread overview]
Message-ID: <200901252325.59905.paul@codesourcery.com> (raw)
In-Reply-To: <20090125195722.GC4799@shareable.org>
On Sunday 25 January 2009, Jamie Lokier wrote:
> Paul Brook wrote:
> > Maybe. You risk having to put an SMP safe lock in the MMIO handler, which
> > would probably do bad things to performance.
>
> Would it? It's just one atomic operation in the non-contention case,
> and MMIO writes could be queued the same way that KVM queues them,
> without needing locks for each individual op.
Depends on the host. Even in the uncontended case grabbing a lock tends to
require fairly strong memory barriers.
Like I said, kvm already exhibits fairly abysmal performance characteristics
in this area. I'm not sure how much write coalescing actually helps in
practice for anything other than VGA. It certainly doesn't help with reads.
Paul
prev parent reply other threads:[~2009-01-25 23:26 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-21 19:28 [Qemu-devel] [6391] Fix nographic mode and VNC Blue Swirl
2009-01-21 19:39 ` Stefano Stabellini
2009-01-21 19:52 ` Blue Swirl
2009-01-21 19:56 ` Stefano Stabellini
2009-01-21 20:03 ` Samuel Thibault
2009-01-21 20:16 ` Blue Swirl
2009-01-21 20:29 ` Samuel Thibault
2009-01-21 20:44 ` Blue Swirl
2009-01-21 21:33 ` Anthony Liguori
2009-01-22 0:04 ` Paul Brook
2009-01-22 3:31 ` Anthony Liguori
2009-01-22 4:23 ` Paul Brook
2009-01-22 12:36 ` Ian Jackson
2009-01-23 18:59 ` Paul Brook
2009-01-22 15:29 ` Anthony Liguori
2009-01-23 18:20 ` Paul Brook
2009-01-23 19:37 ` Anthony Liguori
2009-01-25 19:57 ` Jamie Lokier
2009-01-25 23:25 ` Paul Brook [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=200901252325.59905.paul@codesourcery.com \
--to=paul@codesourcery.com \
--cc=blauwirbel@gmail.com \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).