On 11/02/2020 23:30, Jens Axboe wrote: > On 2/11/20 1:20 PM, Pavel Begunkov wrote: >> Hi, >> >> I've been looking for hashed io-wq enqueuing, but not fully understand the >> issue. As I remember, it was something about getting around blocking for >> buffered I/O. Is that so? Is there any write-up of a thread for this issue? > > Not sure if there's a writeup, but the issue is that buffered writes all > need to grab the per-inode mutex. Hence if you don't serialize these writes, > you end up having potentially quite a few threads banging on the same mutex. > This causes a high level of lock contention (and scheduling). By serializing > by inode hash we avoid that, and yield the same performance. > > Dave Chinner is working on lifting this restriction, at which point we'll > have to gate the hashing based on whether or not the fs is smart or dumb > when it comes to buffered writes and locking. Got it, thanks! >> My case is 2-fd request, and I'm not sure how it should look. For splice() it's >> probably Ok to hash the non-pipe end (if any), but I wonder how it should work, >> if, for example, the restriction will be removed. > > Probably just do the same, but for the output fd only (and following the > same restrictions in terms of file type). > -- Pavel Begunkov
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