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* Re: [PATCH] Re: Negative scalability by removal of  lock_kernel()?(Was:Strange performance behavior of 2.4.0-test9)
@ 2000-11-05  4:19 Dave Wagner
  0 siblings, 0 replies; 18+ messages in thread
From: Dave Wagner @ 2000-11-05  4:19 UTC (permalink / raw)
  To: torvalds; +Cc: linux-kernel

Linus Torvalds wrote:
>
> No.
>
> Please use unserialized accept() _always_, because we can fix that.
>
> Even 2.2.x can be fixed to do the wake-one for accept(), if required.
> It's not going to be any worse than the current apache config, and
> basically the less games apache plays, the better the kernel can try to
> accomodate what apache _really_ wants done.  When playing games, you
> hide what you really want done, and suddenly kernel profiles etc end up
> being completely useless, because they no longer give the data we needed
> to fix the problem.
>
> Basically, the whole serialization crap is all about the Apache people
> saying the equivalent of "the OS does a bad job on something we consider
> to be incredibly important, so we do something else instead to hide it".
>
> And regardless of _what_ workaround Apache does, whether it is the sucky
> fcntl() thing or using SysV semaphores, it's going to hide the real
> issue and mean that it never gets fixed properly.
>
> And in the end it will result in really really bad performance.
>
> Instead, if apache had just done the thing it wanted to do in the first
> place, the wake-one accept() semantics would have happened a hell of a
> lot earlier.
>
> Now it's there in 2.4.x. Please use it. PLEASE PLEASE PLEASE don't play
> games trying to outsmart the OS, it will just hurt Apache in the long run.
>

But how would you suggest people using 2.2 configure their
Apache?  Will flock/fcntl or semaphores perform better (albeit
"uglier") than unserialized accept()'s in 2.2.  I'm willing
and expecting to rebuild apache when 2.4 is released.  I do
not, though, want to leave performance on the table today,
just so I can say that my apache binary is 2.4-ready.

Do any of the apache serialization methods (flock/fcntl/semops)
have any performance improvement over unserialized accept() with
Apache running on a 2.2 kernel?

Dave Wagner

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^ permalink raw reply	[flat|nested] 18+ messages in thread
* Re: Negative scalability by removal of lock_kernel()?(Was: Strange  performance behavior of 2.4.0-test9)
@ 2000-10-27  6:32 Jeff V. Merkey
  2000-10-27  7:13 ` Alexander Viro
  0 siblings, 1 reply; 18+ messages in thread
From: Jeff V. Merkey @ 2000-10-27  6:32 UTC (permalink / raw)
  To: kumon; +Cc: Rik van Riel, linux-kernel


Linux has lots of n-sqared linear list searches all over the place, and
there's a ton of spots I've seen it go linear by doing fine grained
manipulation of lock_kernel() [like in BLOCK.C in NWFS for sending async
IO to ll_rw_block()].   I could see where there would be many spots
where playing with this would cause problems.  

2.5 will be better.

Jeff

kumon@flab.fujitsu.co.jp wrote:
> 
> Finally, I found:
> Removal of lock_kernel in fs/fcntl.c causes the strange performance of
> 2.4.0-test9.
> 
> The removal causes following negative scalability on Apache-1.3.9:
>         * 8-way performance dropped to 60% of 4-way performance.
>         * Adding lock_kernel() gains 2.4x performance on 8-way.
> 
> This suggests some design malfunction exist in the fs-code.
> 
> The lock_kernel() is removed in test9, as shown in below, then the
> strange behavior appeared.
> 
> linux-2.4.0-test8/fs/fcntl.c:
> asmlinkage long sys_fcntl(unsigned int fd, unsigned int cmd, unsigned long arg)
> {
>         struct file * filp;
>         long err = -EBADF;
> 
>         filp = fget(fd);
>         if (!filp)
>                 goto out;
> 
> -->     lock_kernel();
>         err = do_fcntl(fd, cmd, arg, filp);
> -->     unlock_kernel();
> 
>         fput(filp);
> out:
>         return err;
> }
> 
> Adding the lock_kernel()/unlock_kernel() to test9:fs/fcntl.c,
>         The performance is restored,
>         The number of task switch is reduced, and
>         Positive scalability is observed.
> 
> The lock region may be narrowed to around call of posix_lock_file()
> in fcntl_setlk() (fs/locks.c).
> 
> I usually prefer removal of kernel_lock, but at this time,
> the removal severy struck the performance.
> 
> Please give me suggestions..
> 
> kumon@flab.fujitsu.co.jp writes:
>  > kumon@flab.fujitsu.co.jp writes:
>  >  > Rik van Riel writes:
>  >  >  > On Wed, 25 Oct 2000 kumon@flab.fujitsu.co.jp wrote:
>  >  >  > > I found very odd performance behavior of 2.4.0-test9 on a large SMP
>  >  >  > > server, and I want some clues to investigate it.
>  >  >  > >
>  >  >  > > 1) At the 8 cpu configuration, test9 shows extremely inferior
>  >  >  > >    performance.
>  >  >  > > 2) on test8, 8-cpu configuration shows about 2/3 performance of 4-cpu.
>  >  >  >         ^^^^^ test9 ??
>  >
>  > IMHO, the modification of file-system code causes the weird
>  > performance.
>  >
>  > Most of processes are slept at:
>  >      posix_lock_file()->locks_block_on()->interruptible_sleep_on_locks()
>  >
>  > We revert two of test9 files (fs/fcntl.c fs/flock.c), to the previous
>  > version, the performance problem disappeared and it becomes to the
>  > same level as test8.
>  >
>  > To narrow the problem, we measured performance of 3 configuration:
>  > 1) test9 with test8 fs/fcntl.c, test8 fs/flock.c
>  > 2) test9 with test8 fs/fcntl.c
>  > 3) test9 with test8 fs/flock.c
>  >
>  > Only 3) shows the problem, so the main problem reside in fcntl.c (not
>  > in flock.c).
>  >
>  > So it seems:
>  > the web-server, apache-1.3.9 in the redhat-6.1, issues lots of fcntl
>  > to the file and those fcntls collide each other, and the processes
>  > are blocked.
>  >
>  >
>  > What has happend to fcntl.c?
>  >
>  > --
>  > Computer Systems Laboratory, Fujitsu Labs.
>  > kumon@flab.fujitsu.co.jp
> -
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^ permalink raw reply	[flat|nested] 18+ messages in thread
end of thread, other threads:[~2000-11-05  4:23 UTC | newest]

Thread overview: 18+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2000-11-05  4:19 [PATCH] Re: Negative scalability by removal of lock_kernel()?(Was:Strange performance behavior of 2.4.0-test9) Dave Wagner
  -- strict thread matches above, loose matches on Subject: below --
2000-10-27  6:32 Negative scalability by removal of lock_kernel()?(Was: Strange " Jeff V. Merkey
2000-10-27  7:13 ` Alexander Viro
2000-10-27  7:46   ` Andi Kleen
2000-10-27 10:23     ` Andrew Morton
2000-10-27 12:57       ` [PATCH] " kumon
2000-10-28 15:46         ` Andrew Morton
2000-10-28 15:58           ` Andi Kleen
2000-10-28 16:05           ` Jeff Garzik
2000-10-28 16:46           ` Andrew Morton
2000-10-30  9:27             ` kumon
2000-10-30 15:00               ` Andrew Morton
2000-10-30 23:24                 ` dean gaudet
2000-11-04  5:08                   ` [PATCH] Re: Negative scalability by removal of lock_kernel()?(Was:Strange " Andrew Morton
2000-11-04  6:23                     ` Linus Torvalds
2000-11-04 20:03                       ` dean gaudet
2000-11-04 20:11                     ` dean gaudet
2000-10-31 15:36         ` [PATCH] Re: Negative scalability by removal of lock_kernel()?(Was: Strange " Andrew Morton
2000-11-01  1:02           ` kumon
2000-11-02 11:09           ` kumon
2000-11-02 12:50             ` kumon
2000-11-04  5:07             ` Andrew Morton

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