From: Tristan Gingold <gingold@adacore.com>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
Jan Kiszka <jan.kiszka@siemens.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
Anthony Liguori <aliguori@linux.vnet.ibm.com>,
Paul Brook <paul@codesourcery.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"Edgar E. Iglesias" <edgar.iglesias@gmail.com>,
Aurelien Jarno <aurelien@aurel32.net>,
Arun Bharadwaj <arun@linux.vnet.ibm.com>
Subject: Re: [Qemu-devel] Re: [PATCH 2/7] Enable I/O thread and VNC threads by default
Date: Tue, 8 Feb 2011 12:07:02 +0100 [thread overview]
Message-ID: <FFECADA4-4C93-4D69-9E66-7F9B2B08685C@adacore.com> (raw)
In-Reply-To: <4D51842C.8000209@codemonkey.ws>
On Feb 8, 2011, at 6:58 PM, Anthony Liguori wrote:
> On 02/08/2011 04:06 AM, Aurelien Jarno wrote:
>> Yes, it's slow. But is it a problem? You assume that people use QEMU
>> only for emulating SMP platforms. This is a wrong assumption. Beside the
>> x86 target, only sparc really supports SMP emulation.
>>
>
> It's *not* just about performance.
>
> TCG requires a signal to break out of a tight chained TB loop. If you have a guest in a tight loop waiting for something external (like polling on a in-memory flag), the device emulation will not get to run until a signal is fired.
>
> Unless you set SIGIO on every file descriptor that selects polls on (and you can't because there are a number that just don't support SIGIO), then you have a race condition.
A race condition ? Looks like you are describing a dead-lock.
But the dead lock doesn't happen because of the timer which periodically exits from TCG. Hence the performance issue.
> This can be fixed by running TCG in a separate thread than select() and sending a signal to the TCG VCPU when select() returns (effectively SIGIO in userspace).
>
> This is exactly what the I/O thread does.
(Nobody was able to make it working on Windows - or nobody was interested in ?)
Tristan.
next prev parent reply other threads:[~2011-02-08 11:07 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-24 21:00 [Qemu-devel] [RFC 0/7] Introduce hard dependency on glib Anthony Liguori
2011-01-24 21:00 ` [Qemu-devel] [PATCH 1/7] io-thread: make sure to initialize qemu_work_cond and qemu_cpu_cond Anthony Liguori
2011-02-08 8:53 ` [Qemu-devel] " Jan Kiszka
2011-02-08 9:01 ` Anthony Liguori
2011-01-24 21:00 ` [Qemu-devel] [PATCH 2/7] Enable I/O thread and VNC threads by default Anthony Liguori
2011-01-24 22:28 ` [Qemu-devel] " Anthony Liguori
2011-01-25 9:17 ` Edgar E. Iglesias
2011-01-25 13:34 ` Marcelo Tosatti
2011-02-07 10:12 ` Marcelo Tosatti
2011-02-07 16:03 ` Marcelo Tosatti
2011-02-07 16:23 ` Paolo Bonzini
2011-02-07 17:10 ` Jan Kiszka
2011-02-07 21:02 ` Anthony Liguori
2011-02-07 21:45 ` Aurelien Jarno
2011-02-08 2:09 ` Anthony Liguori
2011-02-08 7:26 ` Aurelien Jarno
2011-02-08 8:08 ` Paolo Bonzini
2011-02-08 8:50 ` Jan Kiszka
2011-02-08 9:05 ` Aurelien Jarno
2011-02-08 9:12 ` Anthony Liguori
2011-02-08 9:49 ` Paolo Bonzini
2011-02-08 9:51 ` Jan Kiszka
2011-02-08 9:58 ` Aurelien Jarno
2011-02-08 10:03 ` Jan Kiszka
2011-02-08 10:06 ` Aurelien Jarno
2011-02-08 10:16 ` Alexander Graf
2011-02-08 10:17 ` Stefan Hajnoczi
2011-02-08 10:27 ` Aurelien Jarno
2011-02-08 10:31 ` Paolo Bonzini
2011-02-08 10:40 ` Jan Kiszka
2011-02-08 18:05 ` Anthony Liguori
2011-02-08 11:29 ` Aurelien Jarno
2011-02-08 12:38 ` Riku Voipio
2011-02-08 10:21 ` Jan Kiszka
2011-02-08 10:26 ` Aurelien Jarno
2011-02-08 10:30 ` Jan Kiszka
2011-02-08 17:58 ` Anthony Liguori
2011-02-08 11:07 ` Tristan Gingold [this message]
2011-02-08 11:46 ` Aurelien Jarno
2011-02-08 12:07 ` Paolo Bonzini
2011-02-08 19:21 ` Anthony Liguori
2011-02-08 11:15 ` Aurelien Jarno
2011-02-08 12:10 ` Paolo Bonzini
2011-02-08 13:31 ` Aurelien Jarno
2011-02-08 15:08 ` Aurelien Jarno
2011-02-09 17:35 ` Aurelien Jarno
2011-02-09 20:07 ` Anthony Liguori
2011-02-11 0:03 ` Marcelo Tosatti
2011-02-08 19:17 ` Anthony Liguori
2011-02-08 13:30 ` Aurelien Jarno
2011-02-08 20:54 ` Anthony Liguori
2011-02-08 15:09 ` Aurelien Jarno
2011-02-09 17:13 ` Blue Swirl
2011-02-09 22:16 ` [Qemu-devel] " Stefan Weil
2011-02-10 7:34 ` Paolo Bonzini
2011-02-10 9:54 ` Paolo Bonzini
2011-02-10 19:46 ` Stefan Weil
2011-02-08 10:06 ` [Qemu-devel] " Paolo Bonzini
2011-02-07 18:35 ` Edgar E. Iglesias
2011-02-07 20:44 ` Aurelien Jarno
2011-02-07 21:30 ` Scott Wood
2011-02-07 20:47 ` Edgar E. Iglesias
2011-01-25 8:33 ` [Qemu-devel] [PATCH 0/2] vnc: the lost parts Corentin Chary
2011-01-25 8:33 ` [Qemu-devel] [PATCH 1/2] vl.c: set NULL upon deleting handlers in qemu_set_fd_handler2() Corentin Chary
2011-01-25 10:03 ` Stefan Hajnoczi
2011-01-25 10:13 ` Corentin Chary
2011-01-25 10:26 ` Stefan Hajnoczi
2011-01-25 12:05 ` Yoshiaki Tamura
2011-01-25 8:33 ` [Qemu-devel] [PATCH 2/2] vnc: qemu can die if the client is disconnected while updating screen Corentin Chary
2011-01-24 21:00 ` [Qemu-devel] [PATCH 3/7] Add support for glib based threading and convert qemu thread to use it Anthony Liguori
2011-01-25 14:24 ` Aurelien Jarno
2011-01-25 15:34 ` Anthony Liguori
2011-02-02 17:32 ` [Qemu-devel] " Paolo Bonzini
2011-02-02 17:35 ` Anthony Liguori
2011-01-24 21:00 ` [Qemu-devel] [PATCH 4/7] Get rid of QemuMutex and teach its callers about GStaticMutex Anthony Liguori
2011-01-24 22:24 ` [Qemu-devel] " Jan Kiszka
2011-01-25 0:02 ` Anthony Liguori
2011-01-25 7:39 ` Jan Kiszka
2011-01-24 21:00 ` [Qemu-devel] [PATCH 5/7] threads: get rid of QemuCond and teach callers about GCond Anthony Liguori
2011-01-24 21:00 ` [Qemu-devel] [PATCH 6/7] Teach vnc server to use GThread directly Anthony Liguori
2011-01-26 10:39 ` Stefan Hajnoczi
2011-01-24 21:00 ` [Qemu-devel] [PATCH 7/7] Rename QemuThread to QemuSThread to indicate that it is not a generic thread Anthony Liguori
2011-01-24 21:28 ` [Qemu-devel] Re: [RFC 0/7] Introduce hard dependency on glib Paolo Bonzini
2011-01-24 22:01 ` Anthony Liguori
2011-01-25 10:41 ` Paolo Bonzini
2011-01-25 11:14 ` Daniel P. Berrange
2011-01-25 11:21 ` Paolo Bonzini
2011-01-25 0:24 ` [Qemu-devel] " Anthony Liguori
2011-01-25 6:51 ` Edgar E. Iglesias
2011-01-25 10:24 ` Stefan Hajnoczi
2011-01-25 11:51 ` Gerd Hoffmann
2011-01-25 12:04 ` Daniel P. Berrange
2011-01-25 14:48 ` Stefano Stabellini
2011-01-25 17:48 ` Anthony Liguori
2011-01-25 18:12 ` Stefano Stabellini
2011-01-25 14:23 ` Aurelien Jarno
2011-01-25 15:35 ` Anthony Liguori
[not found] ` <20110126044710.GU9566@redhat.com>
2011-01-26 15:53 ` Anthony Liguori
2011-01-26 21:23 ` Stefan Hajnoczi
2011-01-26 22:12 ` Anthony Liguori
2011-01-26 17:48 ` Johannes Stezenbach
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