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Re: [Qemu-devel] [PATCH] block: add the support to drain throttled reque
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests |
Date: |
Tue, 27 Mar 2012 07:52:59 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Mar 27, 2012 at 12:29:09PM +0800, Zhi Yong Wu wrote:
> On Mon, Mar 26, 2012 at 10:21 PM, Stefan Hajnoczi <address@hidden> wrote:
> > On Tue, Mar 20, 2012 at 11:44 AM, Stefan Hajnoczi
> > <address@hidden> wrote:
> >> On Tue, Mar 20, 2012 at 10:58:10AM +0100, Kevin Wolf wrote:
> >>> Am 20.03.2012 10:47, schrieb Paolo Bonzini:
> >>> > Il 20/03/2012 10:40, Zhi Yong Wu ha scritto:
> >>> >> HI, Kevin,
> >>> >>
> >>> >> We hope that I/O throttling can be shipped without known issue in QEMU
> >>> >> 1.1, so if you are available, can you give this patch some love?
> >>> >
> >>> > I'm sorry to say this, but I think I/O throttling is impossible to save.
> >>> > As it is implemented now, it just cannot work in the presence of
> >>> > synchronous I/O, except at the cost of busy waiting with the global
> >>> > mutex taken. See the message from Stefan yesterday.
> >>>
> >>> qemu_aio_flush() is busy waiting with the global mutex taken anyway, so
> >>> it doesn't change that much.
> >>
> >> Yesterday I only posted an analysis of the bug but here are some
> >> thoughts on how to move forward. Throttling itself is not the problem.
> >> We've known that synchronous operations in the vcpu thread are a problem
> >> long before throttling. This is just another reason to convert device
> >> emulation to use asynchronous interfaces.
> >>
> >> Here is the list of device models that perform synchronous block I/O:
> >> hw/fdc.c
> >> hw/ide/atapi.c
> >> hw/ide/core.c
> >> hw/nand.c
> >> hw/onenand.c
> >> hw/pflash_cfi01.c
> >> hw/pflash_cfi02.c
> >> hw/sd.c
> >>
> >> Zhi Hui Li is working on hw/fdc.c and recently sent a patch.
> >>
> >> I think it's too close to QEMU 1.1 to convert all the remaining devices
> >> and test them properly before the soft-freeze. But it's probably
> >> possible to convert IDE before the soft-freeze.
> >>
> >> In the meantime we could add this to bdrv_rw_co():
> >>
> >> if (bs->io_limits_enabled) {
> >> fprintf(stderr, "Disabling I/O throttling on '%s' due "
> >> "to synchronous I/O\n", bdrv_get_device_name(bs));
> >> bdrv_io_limits_disable(bs);
> >> }
> >>
> >> It's not pretty but tells the user there is an issue and avoids
> >> deadlocking.
> >
> > No one has commented on this suggestion. I think leaving a known hang
> > in QEMU 1.1 is undesirable. Better to have this warning and disable
> > throttling in the case we cannot support right now.
> IDE is using both sync API and async API when guest boot.
Yes, a warning patch must handle the synchronous I/O case during startup
(guessing disk geometry), which I think happens even for virtio-blk.
Stefan
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, (continued)
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Chris Webb, 2012/03/22
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Stefan Hajnoczi, 2012/03/23
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Chris Webb, 2012/03/23
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Stefan Hajnoczi, 2012/03/23
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Richard Davies, 2012/03/23
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Stefan Hajnoczi, 2012/03/23
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Stefan Hajnoczi, 2012/03/23
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Stefan Hajnoczi, 2012/03/26
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Kevin Wolf, 2012/03/26
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Zhi Yong Wu, 2012/03/27
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests,
Stefan Hajnoczi <=
Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Kevin Wolf, 2012/03/20