On Tue, Feb 12, 2019 at 5:38 PM Raghavendra Gowdappa <rgowdapp@xxxxxxxxxx> wrote:
All,We've found perf xlators io-cache and read-ahead not adding any performance improvement. At best read-ahead is redundant due to kernel read-ahead
One thing we are still figuring out is whether kernel read-ahead is tunable. From what we've explored, it _looks_ like (may not be entirely correct), ra is capped at 128KB. If that's the case, I am interested in few things:
* Are there any realworld applications/usecases, which would benefit from larger read-ahead (Manoj says block devices can do ra of 4MB)?
* Is the limit on kernel ra tunable a hard one? IOW, what does it take to make it to do higher ra? If its difficult, can glusterfs read-ahead provide the expected performance improvement for these applications that would benefit from aggressive ra (as glusterfs can support larger ra sizes)?
I am still inclined to prefer kernel ra as I think its more intelligent and can identify more sequential patterns than Glusterfs read-ahead [1][2].
and at worst io-cache is degrading the performance for workloads that doesn't involve re-read. Given that VFS already have both these functionalities, I am proposing to have these two translators turned off by default for native fuse mounts.For non-native fuse mounts like gfapi (NFS-ganesha/samba) we can have these xlators on by having custom profiles. Comments?regards,Raghavendra
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