Commit 55d85384 authored by Linus Torvalds's avatar 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: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 481c5346
......@@ -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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