Re: [PATCH 0/5] Add vhost-blk support

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tue, Jul 17, 2012 at 12:26 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> On Tue, Jul 17, 2012 at 12:11:15PM +0100, Stefan Hajnoczi wrote:
>> On Tue, Jul 17, 2012 at 10:21 AM, Asias He <asias@xxxxxxxxxx> wrote:
>> > On 07/17/2012 04:52 PM, Paolo Bonzini wrote:
>> >>
>> >> Il 17/07/2012 10:29, Asias He ha scritto:
>> >>>
>> >>> So, vhost-blk at least saves ~6 syscalls for us in each request.
>> >>
>> >>
>> >> Are they really 6?  If I/O is coalesced by a factor of 3, for example
>> >> (i.e. each exit processes 3 requests), it's really 2 syscalls per request.
>> >
>> >
>> > Well. I am counting the number of syscalls in one notify and response
>> > process. Sure the IO can be coalesced.
>>
>> Linux AIO also supports batching in io_submit() and io_getevents().
>> Depending on the request pattern in the vring when you process it, you
>> should be able to do better than 1 set of syscalls per host I/O
>> request.
>>
>> Are you taking advantage of that at the moment in your userspace benchmark?
>>
>> Stefan
>
> Injecting an interrupt directly from kernel bypasses two context switches.
> Yes some worloads can coalesce interrupts efficiently but others can't.
> It is not really hard to speculate more.
>
> Personally I don't understand where all this speculation leads us.
> Are you guys disputing the measurements posted? If not would not
> it be better if discussion focused on the amount of extra code versus
> measured gain?

5-15% is nice.  But what causes the performance advantage?

Knowing the answer to that is important before anyone can say whether
this approach is good or not.

Stefan
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux