[stgt] [PATCH 1/1] null backing store

[Alexander Nezhinsky]

Sorry, I missed the list in my previous reply...

On Thu, Aug 28, 2008 at 2:09 AM, FUJITA Tomonori
<fujita.tomonori at lab.ntt.co.jp> wrote:
> On Wed, 27 Aug 2008 20:22:42 +0300
> "Alexander Nezhinsky" <nezhinsky at gmail.com> wrote:
>> On Wed, Aug 27, 2008 at 8:01 PM, FUJITA Tomonori
>> <fujita.tomonori at lab.ntt.co.jp> wrote:
>>
>> > Thanks. But you can do faster. This patch incurs the thread and pipe
>> > notification overheads. You don't need bs_thread stuff. See bs_aio.c
>>
>> Sure. I intended to do it that way later. I'm going to send some performance
>> results over ISER in a couple of days, so i first used this
>> straightforward implementation.
>
> Nice.
>
>> Moreover, it is also interesting to measure *with* the thread'n'pipe
>> overhead because
>> this way you only exclude I/O. It can be later compared with a version
>> without threads
>> to assess their impact.
>
> Yeah, the results should be interesting because we plan to remove the
> thread mechanism (well, we need to wait for the AIO support in Linux
> kernel).
>
>> > After that, you can do more faster. You can use sendfile (send data
>> > without memory copy) though you need some changes to the core code.
>>
>> How is sendfile() applicable to this null i/o backing store? I am not
>> sending anything
>> to I/O anyway, so there is no memory copy to spare.
>
> You send data to an initiator without doing disk I/Os.
>
> Anyway, you are an iSER guy, so you can forget sendfile stuff.

You mean sendfile /dev/zero --> socket or socket -->  /dev/null in case of
iSCSI/TCP, don't you?
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