On 06 Sep 2013, at 4:10 PM, Ed Cashin <ecas...@coraid.com> wrote:
> I don't have a lot of experience with the other non-Coraid AoE targets that
> are out there, but you might check whether one of them that's oriented more
> toward performance could be useful to you.
>
> That said, while checking the vblade README for the design goals, I noticed
> that it advertises a capacity for 16 outstanding commands. If you want to
> try some tuning, you could adjust Bufcount in dat.h and then make sure your
> settings in /proc are sufficient to allow the kernel to buffer 16 writes.
> (Read commands are small.)
I ran vblade with -b to increase the buffer count and it improved performance
quite a bit, but it's now maxing out the CPU. I found that bufcount above 64
showed little or no improvement. There is however a big difference between
using normal IO (dd with conv=fdatasync) and direct IO (dd with
{o,i}flag=direct) on the initiator:
Test MB/s CPU AvgPktSz Direct MB/s CPU AvgPktSz
Disk Read 538 95% 2083 623 67% 4333
Disk Write 443 97% 2095 582 75% 4345
Ramdisk Read 655 97% 2083 778 69% 4333
Ramdisk Write 424 100% 2095 624 81% 4345
AvgPktSz shows the average packet size as measured by nettop. Wireshark
confirms that "normal" IO generates 4132-byte packets while direct IO results
in 8740-byte packets. I know Q 5.23 of the Coraid Linux FAQ says that AoE
devices with an odd number of sectors result in 512-byte IO jobs, but mine have
even sector counts. This is probably not the best way to benchmark but when I
create a filesystem on top of my AoE device I get awful performance (50 MB/s)
so there are obviously alignment issues.
Either way, looking at the CPU usage it's clear that vblade isn't going reach
10 Gb/s.
I also tried other Linux targets:
kvblade: Doesn't compile against kernel 3.x.
ggaoed: About 25% slower than vblade:
Test MB/s CPU Direct MB/s CPU
Disk Read 446 71% 446 51%
Disk Write 355 63% 557 56%
Ramdisk Read 531 91% 627 67%
Ramdisk Write 399 85% 602 73%
qaoed: 25 - 50% slower than vblade:
Test MB/s CPU Direct MB/s CPU
Disk Read 282 77% 473 73%
Disk Write 259 85% 465 73%
Ramisk Read 291 99% 521 69%
Ramdisk Write 261 75% 467 75%
Unless I'm missing any further tuning options, none of the open source Linux
AoE targets seem to be suitable for a 10 Gb/s SAN.
Regards,
Derick
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