[Bugs] [Bug 1665029] read-ahead and io-cache degrading performance on sequential read

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1665029



--- Comment #3 from Raghavendra G <rgowdapp at redhat.com> ---
(In reply to Raghavendra G from comment #2)
> Some observations while debugging the performance degradation with gluster
> read-ahead:
> 
> * Kernel too does read-ahead and it sends parallel read-requests as part of
> this.
> * client-io-threads is on in this configuration.
> 
> The above two points mean parallel requests sent by kernel can reach
> read-ahead out of order. This means read-ahead no longer sees read requests
> at sequential contiguous offsets and hence it things reads are random. For
> random reads, it resets the read sequence. But when requests reach
> read-ahead in order, read-ahead is turned on again. Due to this intermittent
> toggling, much of read-ahead data is wasted regressing the performance. With
> client-io-threads off and I can no longer see the regression for the test
> case given. If I run the test with single fio job (--numjobs=1), gluster
> read-ahead on outperforms gluster read-ahead off on my setup.

... single fio job (--numjobs=1), gluster read-ahead on with client-io-threads
off outperforms gluster read-ahead off with client-io-threads off.

> 
> [1] https://review.gluster.org/#/c/glusterfs/+/20981/

-- 
You are receiving this mail because:
You are on the CC list for the bug.