Re: [Qemu-devel] [PATCH V4 10/12] SD card users: optimize access to SDClass methods

[Igor Mitsyanko]

On 07/31/2012 07:43 PM, Peter Maydell wrote:
> On 27 July 2012 20:29, Igor Mitsyanko <address@hidden> wrote:
> > Rather that repeatedly call SD_GET_CLASS() in a loop, call it once before
> > a loop starts.
> Anthony claims that SD_GET_CLASS should be cheap enough that we don't
> need to hoist it out of loops like this. Do you have profiling data
> or similar that caused you to write this patch?
>
> -- PMM
Well, I've tested it by measuring an execution time of a 4Kb write to SD 
card, results showed that arithmetic mean of time for one 4k write was 
less by ~300us in sequence with SD_GET_CLASS extracted from the loop. 
Although I ran this test several times, I have little faith in test 
methodology and results, it obviously showed significant dispersion 
between measured time of distinct 4K writes (200-300% if I recall 
correctly). I really have no objection no objection to dropping this patch.