Re: [Qemu-devel] [PATCH v8 3/4] block: add block timer and throttling algorithm

[Stefan Hajnoczi]

On Mon, Oct 17, 2011 at 11:26 AM, Kevin Wolf <address@hidden> wrote:
> Am 26.09.2011 09:24, schrieb Zhi Yong Wu:
>> On Sat, Sep 24, 2011 at 12:19 AM, Kevin Wolf <address@hidden> wrote:
>>> Am 08.09.2011 12:11, schrieb Zhi Yong Wu:
>>>> Note:
>>>>      1.) When bps/iops limits are specified to a small value such as 511 
>>>> bytes/s, this VM will hang up. We are considering how to handle this 
>>>> senario.
>>>>      2.) When "dd" command is issued in guest, if its option bs is set to 
>>>> a large value such as "bs=1024K", the result speed will slightly bigger 
>>>> than the limits.
>>>>
>>>> For these problems, if you have nice thought, pls let us know.:)
>>>>
>>>> Signed-off-by: Zhi Yong Wu <address@hidden>
>>>> ---
>>>>  block.c |  259 
>>>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>>>>  block.h |    1 -
>>>>  2 files changed, 248 insertions(+), 12 deletions(-)
>>>
>>> One general comment: What about synchronous and/or coroutine I/O
>>> operations? Do you think they are just not important enough to consider
>>> here or were they forgotten?
>> For sync ops, we assume that it will be converse into async mode at
>> some point of future, right?
>> For coroutine I/O, it is introduced in image driver layer, and behind
>> bdrv_aio_readv/writev. I think that we need not consider them, right?
>
> Meanwhile the block layer has been changed to handle all requests in
> terms of coroutines. So you would best move your intercepting code into
> the coroutine functions.

Some additional info: the advantage of handling all requests in
coroutines is that there is now a single place where you can put I/O
throttling.  It will work for bdrv_read(), bdrv_co_readv(), and
bdrv_aio_readv().  There is no code duplication, just put the I/O
throttling logic in bdrv_co_do_readv().

Stefan