Messages in this thread | | | Date | Tue, 21 Oct 2003 03:59:00 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH][2.6-mm] Avoid flushing AIO workqueue on cancel/exit |
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Suparna Bhattacharya <suparna@in.ibm.com> wrote: > > When streaming AIO requests are in progress on multiple > io context's, flushing the AIO workqueue on i/o cancellation > or process exit could potentially end up waiting for a > long time as fresh requests from other active ioctx's keep > getting queued up.
But flush_workqueue() will ignore any newly-added work requests:
* This function will sample each workqueue's current insert_sequence number and * will sleep until the head sequence is greater than or equal to that. This * means that we sleep until all works which were queued on entry have been * handled, but we are not livelocked by new incoming ones.
Now, flush_workqueue() is potentially inefficient on SMP because it flushes each CPU's workqueue sequentially. But we can fix that in flush_workqueue() by converting it to a two-pass approach:
a) gather each CPU's insert_sequence number into a local array[NR_CPUS]
b) wait until each CPU's remove_sequence number exceeds the previously-gathered insert_sequence number.
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