Re: Performance of SCST versus STGT

[Vladislav Bolkhovitin]

FUJITA Tomonori wrote:

On Tue, 22 Jan 2008 14:33:13 +0300
Vladislav Bolkhovitin <[EMAIL PROTECTED]> wrote:

FUJITA Tomonori wrote:

The big problem of stgt iSER is disk I/Os (move data between disk and
page cache). We need a proper asynchronous I/O mechanism, however,
Linux doesn't provide such and we use a workaround, which incurs large
latency. I guess, we cannot solve this until syslets is merged into
mainline.

Hmm, SCST also doesn't have ability to use asynchronous I/O, but that doesn't prevent it from showing good performance.

I don't know how SCST performs I/Os, but surely, in kernel space, you
can performs I/Os asynchronously.

Sure, but currently it all synchronous

Or you use an event notification
mechanism with multiple kernel threads performing I/Os synchronously.

Xen blktap has the same problem as stgt. IIRC, Xen mainline uses a
kernel patch to add a proper event notification to AIO though redhat
uses the same workaround as stgt instead of applying the kernel patch.
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