FUJITA Tomonori wrote:
On Tue, 29 Jan 2008 13:31:52 -0800
Roland Dreier <[EMAIL PROTECTED]> wrote:
> . . STGT read SCST read . STGT read
SCST read .
> . . performance performance . performance
performance .
> . . (0.5K, MB/s) (0.5K, MB/s) . (1 MB, MB/s)
(1 MB, MB/s) .
> . iSER (8 Gb/s network) . 250 N/A . 360
N/A .
> . SRP (8 Gb/s network) . N/A 421 . N/A
683 .
> On the comparable figures, which only seem to be IPoIB they're showing a
> 13-18% variance, aren't they? Which isn't an incredible difference.
Maybe I'm all wet, but I think iSER vs. SRP should be roughly
comparable. The exact formatting of various messages etc. is
different but the data path using RDMA is pretty much identical. So
the big difference between STGT iSER and SCST SRP hints at some big
difference in the efficiency of the two implementations.
iSER has parameters to limit the maximum size of RDMA (it needs to
repeat RDMA with a poor configuration)?
Anyway, here's the results from Robin Humble:
iSER to 7G ramfs, x86_64, centos4.6, 2.6.22 kernels, git tgtd,
initiator end booted with mem=512M, target with 8G ram
direct i/o dd
write/read 800/751 MB/s
dd if=/dev/zero of=/dev/sdc bs=1M count=5000 oflag=direct
dd of=/dev/null if=/dev/sdc bs=1M count=5000 iflag=direct
Both Robin (iser/stgt) and Bart (scst/srp) using ramfs
Robin's numbers come from DDR IB HCAs
Bart's numbers come from SDR IB HCAs:
Results with /dev/ram0 configured as backing store on the
target (buffered I/O):
Read Write Read
Write
performance performance
performance performance
(0.5K, MB/s) (0.5K, MB/s) (1 MB,
MB/s) (1 MB, MB/s)
STGT + iSER 250 48 349
781
SCST + SRP 411 66 659
746
Results with /dev/ram0 configured as backing store on the
target (direct I/O):
Read Write Read
Write
performance performance
performance performance
(0.5K, MB/s) (0.5K, MB/s) (1 MB,
MB/s) (1 MB, MB/s)
STGT + iSER 7.9 9.8 589
647
SCST + SRP 12.3 9.7 811
794
http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg13514.html
Here are my numbers with DDR IB HCAs, SCST/SRP 5G /dev/ram0
block_io mode, RHEL5 2.6.18-8.el5
direct i/o dd
write/read 1100/895 MB/s
dd if=/dev/zero of=/dev/sdc bs=1M count=5000 oflag=direct
dd of=/dev/null if=/dev/sdc bs=1M count=5000 iflag=direct
buffered i/o dd
write/read 950/770 MB/s
dd if=/dev/zero of=/dev/sdc bs=1M count=5000
dd of=/dev/null if=/dev/sdc bs=1M count=5000
So when using DDR IB hcas:
stgt/iser scst/srp
direct I/O 800/751 1100/895
buffered I/O 1109/350 950/770
-vu
http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg13502.html
I think that STGT is pretty fast with the fast backing storage.
I don't think that there is the notable perfornace difference between
kernel-space and user-space SRP (or ISER) implementations about moving
data between hosts. IB is expected to enable user-space applications
to move data between hosts quickly (if not, what can IB provide us?).
I think that the question is how fast user-space applications can do
I/Os ccompared with I/Os in kernel space. STGT is eager for the advent
of good asynchronous I/O and event notification interfances.
One more possible optimization for STGT is zero-copy data
transfer. STGT uses pre-registered buffers and move data between page
cache and thsse buffers, and then does RDMA transfer. If we implement
own caching mechanism to use pre-registered buffers directly with (AIO
and O_DIRECT), then STGT can move data without data copies.
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