RE: [Scst-devel] ISCSI-SCST performance (with also IET and STGTdata)

[Sufficool, Stanley]

> -----Original Message-----
> From: Bart Van Assche [mailto:bart.vanassche@xxxxxxxxx] 
> Sent: Friday, April 03, 2009 10:09 AM
> To: Vladislav Bolkhovitin
> Cc: scst-devel; linux-kernel@xxxxxxxxxxxxxxx; 
> linux-scsi@xxxxxxxxxxxxxxx
> Subject: Re: [Scst-devel] ISCSI-SCST performance (with also 
> IET and STGTdata)
> 
> 
> On Thu, Apr 2, 2009 at 7:16 PM, Vladislav Bolkhovitin 
> <vst@xxxxxxxx> wrote:
> > Bart Van Assche, on 04/02/2009 12:14 AM wrote:
> >> I have repeated some of these performance tests for iSCSI 
> over IPoIB 
> >> (two DDR PCIe 1.0 ConnectX HCA's connected back to back). 
> The results 
> >> for the buffered I/O test with a block size of 512K (initiator) 
> >> against a file of 1GB residing on a tmpfs filesystem on the target 
> >> are as follows:
> >>
> >> write-test: iSCSI-SCST 243 MB/s; IET 192 MB/s.
> >> read-test: iSCSI-SCST 291 MB/s; IET 223 MB/s.
> >>
> >> And for a block size of 4 KB:
> >>
> >> write-test: iSCSI-SCST 43 MB/s; IET 42 MB/s.
> >> read-test: iSCSI-SCST 288 MB/s; IET 221 MB/s.
> >
> > Do you have any thoughts why writes are so bad? It shouldn't be so..
> 
> It's not impossible that with the 4 KB write test I hit the 
> limits of the initiator system (Intel E6750 CPU, 2.66 GHz, 
> two cores). Some statistics I gathered during the 4 KB write test:
> Target: CPU load 0.5, 16500 mlx4-comp-0 interrupts per 
> second, same number of interrupts processed by each core (8250/s).
> Initiator: CPU load 1.0, 32850 mlx4-comp-0 interrupts per 
> second, all interrupts occurred on the same core.

Are you using connected mode IPoIB and setting the MTU to 4KB? Would
fragmentation of IPoIB drive up the interrupt rates?

> 
> Bart.
> 
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