On 12/11/2015 09:53, Li, Liang Z wrote:
>> On 12/11/2015 03:49, Li, Liang Z wrote:
>>> I am very surprised about the live migration performance result when
>>> I use your ' memeqzero4_paolo' instead of these SSE2 Intrinsics to
>>> check the zero pages.
>>
>> What code were you using? Remember I suggested using only unsigned long
>> checks, like
>>
>> unsigned long *p = ...
>> if (p[0] || p[1] || p[2] || p[3]
>> || memcmp(p+4, p, size - 4 * sizeof(unsigned long)) != 0)
>> return BUFFER_NOT_ZERO;
>> else
>> return BUFFER_ZERO;
>>
>
> I use the following code:
>
>
> bool memeqzero4_paolo(const void *data, size_t length)
> {
> ...
> }
The code you used is very generic and not optimized for the kind of data
you see during migration, hence the existing code in QEMU fares better.
>>> The total live migration time increased about
>>> 8%! Not decreased. Although in the unit test your '
>>> memeqzero4_paolo' has better performance, any idea?
>>
>> You only tested the case of zero pages. But real pages usually are not zero,
>> even if they have a few zero bytes at the beginning. It's very important to
>> optimize the initial check before the memcmp call.
>>
>
> In the unit test, I only test zero pages too, and the performance of
> 'memeqzero4_paolo' is better.
> But when merged into QEMU, it caused performance drop. Why?
Because QEMU is not migrating zero pages only.
Paolo
