Re: sync guest calls made async on host - SQLite performance

[Matthew Tippett <tippettm@gmail.com>]

Thanks Duncan for reproducing the behavior outside myself and Phoronix.

I dug deeper into the actual syscalls being made by sqlite.  The salient 
part of the behaviour is small sequential writes followed by a fdatasync 
(effectively a metadata-free fsync).

As Dustin indicates,

    if scsi is used, you incur the cost of virtualization,
    if virtio is used, your guests fsyncs incur less cost.

So back to the question to the kvm team.  It appears that with the stock 
KVM setup customers who need higher data integrity (through fsync) 
should steer away from virtio for the moment.

Is that assessment correct?

Regards,

Matthew


-------- Original Message  --------
Subject: Re: sync guest calls made async on host - SQLite performance
From: Dustin Kirkland <dustin.kirkland@gmail.com>
To: Matthew Tippett <tippettm@gmail.com>, Anthony Liguori 
<anthony@codemonkey.ws>, Avi Kivity <avi@redhat.com>, RW 
<kvm@tauceti.net>, kvm@vger.kernel.org
Date: 10/09/2009 11:18 AM

> On Fri, Oct 9, 2009 at 6:25 AM, Matthew Tippett <tippettm@gmail.com> wrote:
>> Can I ask you to do the following...
>>
>>  1) Re-affirm that Ubuntu does not carry any non-stream patches and
>> the build command and possibly any other unusual patches or
>> commandline options.  This should push it back onto Avi and Anthony's
>> plate.
> 
> I have put the patches we're carrying here, for your review:
>  * http://rookery.canonical.com/~kirkland/patches
> 
> There's nothing exotic in here.  Most of these have been committed
> upstream already.  All of them have been at least posted on these
> lists.  None of these should affect your test case.
> 
> We configure with:
>   ./configure --prefix=/usr --disable-blobs --audio-drv-list="alsa pa
> oss sdl" --audio-card-list="ac97 es1370 sb16 cs4231a adlib gus"
> --target-list="$(TARGET_SYSTEM_TCG) $(TARGET_LINUX_TCG)"
> 
> We carry a number of compiler options, mostly in the interest of
> hardening and security:
>   * https://wiki.ubuntu.com/CompilerFlags
> 
> The #define'd variables on my local system (which should be similar,
> though not identical to our build servers) can be seen here:
>  * http://rookery.canonical.com/~kirkland/defined
> 
>>  2) Carefully consider risks to virtualized environments in the
>> server space and consider noting it in release notes.
> 
> Thank you for the suggestion.  I will take it under consideration.
> 
> :-Dustin