Commit 55d85384 authored Jun 22, 2008 by Linus Torvalds

Fix performance regression on lmbench select benchmark



Christian Borntraeger reported that reinstating cond_resched() with
CONFIG_PREEMPT caused a performance regression on lmbench:

	For example select file 500:
	23 microseconds
	32 microseconds

and that's really because we totally unnecessarily do the cond_resched()
in the innermost loop of select(), which is just silly.

This moves it out from the innermost loop (which only ever loops ove the
bits in a single "unsigned long" anyway), which makes the performance
regression go away.

Reported-and-tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 481c5346

fs/select.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -249,7 +249,6 @@ int do_select(int n, fd_set_bits fds, s64 timeout)
		retval++;
		}
		}
		cond_resched();
		}
		if (res_in)
		*rinp = res_in;
		@@ -257,6 +256,7 @@ int do_select(int n, fd_set_bits fds, s64 timeout)
		*routp = res_out;
		if (res_ex)
		*rexp = res_ex;
		cond_resched();
		}
		wait = NULL;
		if (retval \|\| !*timeout \|\| signal_pending(current))

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