[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] block: add the support to drain throttled reque
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests |
Date: |
Mon, 26 Mar 2012 16:31:41 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1 |
Am 26.03.2012 16:21, schrieb Stefan Hajnoczi:
> 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.
>
> Kevin: Would you accept a patch like this? Or do you have another
> solution in mind?
No, I don't have any clever short-term solution to offer. Put in
whatever hack you think works best for 1.1.
Kevin
- 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, Kevin Wolf, 2012/03/20
- Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Stefan Hajnoczi, 2012/03/20
- 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 <=
- 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, 2012/03/27
Re: [Qemu-devel] [PATCH] block: add the support to drain throttled requests, Kevin Wolf, 2012/03/20