>On Fri, Feb 26, 2016 at 04:18:55PM -0500, Jeff Moyer wrote:
>> Christoph Hellwig <hch@xxxxxx> writes:
>>
>> > This series allows to selectively enable/disable polling for completions
>> > in the block layer on a per-I/O basis. For this it resurrects the
>> > preadv2/pwritev2 syscalls that Milosz prepared a while ago (and which
>> > are much simpler now due to VFS changes that happened in the meantime).
>> > That approach also had a man page update prepared, which I will resubmit
>> > with the current flags once this series makes it in.
>>
>> It would be helpful for reviewers if you submitted the man page at the
>> same time, in my opinion.
>
>Ok.
>
>> Do you have any plans on adding polling support to the buffered path?
>
>How would that even make sense?
Christoph,
On a page cache miss, poll for the BIO serving the page read instead of waiting for the page lock to be released (from device IRQ handler) ? As long as the application is lucky to get a fast page allocation, similar performance improvements as direct I/Os should be observed, shouldn't it ?
Benefit may be restricted to very random accesses. For reasonably sequential accesses, read-ahead would cover, and obviously, no polling there.
So may be polling could be enabled only if read-ahead is disabled. Interestingly, if the device+bus is really really fast, that could result in minimal performance difference between a page cache hit and a miss...
Best.
>
------------------------
Damien Le Moal, Ph.D.
Sr. Manager, System Software Group, HGST Research,
HGST, a Western Digital company
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