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Re: 2.5.40-mm1
Mala Anand wrote:
>
> ...
> P4 Xeon CPU 1.50 GHz 4-way - hyperthreading disabled
> Src is aligned and dst is misaligned as follows:
>
> Dst 2.5.40 2.5.40+patch 2.5.40+patch++
> Align throughout throughput throughput
> (bytes) KB/sec KB/sec KB/sec
> 0 1360071 1314783 912359
> 1 323674 340447
> 2 329202 336425
> 4 512955 693170
> 8 523223 615097 506641
> 12 517184 558701 553700
> 16 966598 872080 932736
> 32 846937 838514 845178
Note the tremendous slowdown which the P4 suffers when you're not
cacheline aligned. Even 32-byte-aligned is down a lot.
> I see too much variance in the test results so I ran
> each test 3 times. I tried increasing the iterations
> but it did not reduce the variance.
>
> Dst is aligned and src is misaligned as follows:
>
> Dst 2.5.40 2.5.40+patch
> Align throughout throughput
> (bytes) KB/sec KB/sec
> 0 1275372 1029815
> 1 529907 511815
> 2 534811 530850
> 4 643196 627013
> 8 568000 626676
> 12 574468 658793
> 16 631707 635979
> 32 741485 592938
This differs a little from my P4 testing - the rep;movsl approach
seemed OK for 8,16,32 alignment.
But still, that's something we can tune later.
>
> However I have seen using floating point registers instead of integer
> registers on Pentium IV improves performance to a greater extent on
> some alignments. I need to do more testing and then I will create a
> patch for pentium IV.
I believe there are "issues" using those registers in-kernel. Related
to the need to save/restore them, or errata; not too sure about that.
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