Messages in this thread | | | Subject | Re: [RFC PATCH 07/10] pipe: Conditionalise wakeup in pipe_read() [ver #2] | From | Konstantin Khlebnikov <> | Date | Sun, 3 Nov 2019 14:04:23 +0300 |
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On 31/10/2019 19.38, David Howells wrote: > Okay, attached is a change that might give you what you want. I tried my > pipe-bench program (see cover note) with perf. The output of the program with > the patch applied was: > > - pipe 305127298 36262221772 302185181 7887690 > > The output of perf with the patch applied: > > 239,943.92 msec task-clock # 1.997 CPUs utilized > 17,728 context-switches # 73.884 M/sec > 124 cpu-migrations # 0.517 M/sec > 9,330 page-faults # 38.884 M/sec > 885,107,207,365 cycles # 3688822.793 GHz > 1,386,873,499,490 instructions # 1.57 insn per cycle > 311,037,372,339 branches # 1296296921.931 M/sec > 33,467,827 branch-misses # 0.01% of all branches > > And without: > > 239,891.87 msec task-clock # 1.997 CPUs utilized > 22,187 context-switches # 92.488 M/sec > 133 cpu-migrations # 0.554 M/sec > 9,334 page-faults # 38.909 M/sec > 884,906,976,128 cycles # 3688787.725 GHz > 1,391,986,932,265 instructions # 1.57 insn per cycle > 311,394,686,857 branches # 1298067400.849 M/sec > 30,242,823 branch-misses # 0.01% of all branches > > So it did make something like a 20% reduction in context switches.
Ok. Looks promising. Depending on workload reduction might be much bigger.
I suppose buffer resize (grow) makes wakeup unconditionally. Should be ok.
> > David > --- > diff --git a/fs/pipe.c b/fs/pipe.c > index e3d5f7a39123..5167921edd73 100644 > --- a/fs/pipe.c > +++ b/fs/pipe.c > @@ -276,7 +276,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) > size_t total_len = iov_iter_count(to); > struct file *filp = iocb->ki_filp; > struct pipe_inode_info *pipe = filp->private_data; > - int do_wakeup; > + int do_wakeup, wake; > ssize_t ret; > > /* Null read succeeds. */ > @@ -329,11 +329,12 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) > tail++; > pipe->tail = tail; > do_wakeup = 1; > - if (head - (tail - 1) == pipe->max_usage) > + wake = head - (tail - 1) == pipe->max_usage / 2; > + if (wake) > wake_up_interruptible_sync_poll_locked( > &pipe->wait, EPOLLOUT | EPOLLWRNORM); > spin_unlock_irq(&pipe->wait.lock); > - if (head - (tail - 1) == pipe->max_usage) > + if (wake) > kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); > } > total_len -= chars; >
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