Re: [Qemu-devel] [PATCH v1 00/17] dataplane: optimization and multi virtqueue support

[Ming Lei <tom.leiming@gmail.com>]

On 8/16/14, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 14/08/2014 12:46, Kevin Wolf ha scritto:
>> So to finally reply with some numbers... I'm running fio tests based on
>> Ming's configuration on a loop-mounted tmpfs image using dataplane.
>
> I'm not sure tmpfs is a particularly useful comparison, since it doesn't
> support O_DIRECT.  O_DIRECT over ramdisk ("modprobe brd rd_nr=1
> rd_size=524288 max_part=1", either directly or via a filesystem) is
> probably a better benchmark.

If loop is over file from tmpfs, that is fine since loop itself supports
O_DIRECT and the sync ->read()/->write() inside loop driver can
return without block.

I have tested loop over tmpfs file, and can't reproduce Kevin's issue.

>
> Also, I'm not sure how the I/O scheduler works over tmpfs.  A ramdisk
> should just do the right thing.  (Are you using deadline or cfq?)
>
>>                 | Random throughput | Sequential throughput
>> ----------------+-------------------+-----------------------
>> master          | 442 MB/s          | 730 MB/s
>> base            | 453 MB/s          | 757 MB/s
>> bypass (Ming)   | 461 MB/s          | 734 MB/s
>> coroutine       | 468 MB/s          | 716 MB/s
>> bypass (Paolo)  | 476 MB/s          | 682 MB/s
>
> This is pretty large, but it really smells like either a setup problem
> or a kernel bug...
>
> Paolo
>

Thanks,
-- 
Ming Lei