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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Brandon Casey <casey@nrlssc.navy.mil>
Cc: Alex Riesen <raa.lkml@gmail.com>,
	Bevan Watkiss <bevan.watkiss@cloakware.com>,
	Git Mailing List <git@vger.kernel.org>
Subject: Re:
Date: Fri, 8 May 2009 14:49:50 -0700 (PDT)	[thread overview]
Message-ID: <alpine.LFD.2.01.0905081432150.4983@localhost.localdomain> (raw)
In-Reply-To: <OWEdfN5mNBoNl1TcdOvhhNfi_nLsao-aFrHkz_rNtuX_4lqXHisfcQ@cipher.nrlssc.navy.mil>



On Fri, 8 May 2009, Brandon Casey wrote:
> 
> Before (cold cache):
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  98.60    6.365501         111     57432           lstat64
> 
> After (cold cache, no lstat fix, just cache_preload):
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  90.90   23.717981         413     57432           lstat64

Yes, interesting. I really smells like it's all fixed performance and 
there is a single lock around it. That 111us -> 413us increase is very 
consistent with four cores all serializing on the same lock. So it 
parallelizes to all four cores, but then will take exactly as long in 
total.

Quite frankly, 2.6.9 is so old that I have absolutely _no_ memory of what 
we used to do back then. Not that I follow NFS all that much even now - I 
did some of the original page cache and dentry work on the Linux NFS 
client way back when, but that was when I actually used NFS (and we were 
converting everything to the page cache).

I've long since forgotten everything I knew, and I'm just as happy about 
that. But clearly something is bad, and equally clearly it worked much 
better for you a couple of months ago. Which does imply that there's 
probably some centos issues.

Can you ask your MIS people if it would be possible to at least _test_ a 
new kernel? In 2.6.9, I'm quite frankly inclined to just say "it will 
likely never get fixed unless centos knows what it is", but if you test a 
more modern kernel and see similar issues, then I'll be intrigued.

It's kind of sad, but at the same time, NFS was using the BKL up into 
2.6.26 or something like that (about a year ago). And your kernel is 
based on something _much_ older.

That said, even with the BKL, NFS should allow all the actual IO to be 
done in parallel (since the BKL is dropped on scheduling). But it's really 
wasting a _lot_ of CPU time, and that hurts you enormously, even though 
the cold-cache case still seems to win, judging by your other email:

> Best without patch: 6.02 (systime 1.57)
> 
>   0.43user 1.57system 0:06.02elapsed 33%CPU (0avgtext+0avgdata 0maxresident)k
>   5336inputs+0outputs (12major+15472minor)pagefaults 0swaps
> 
> Best with patch (preload_cache,lstat reduction): 2.69 (systime 10.47)
> 
>   0.45user 10.47system 0:02.69elapsed 405%CPU (0avgtext+0avgdata 0maxresident)k
>   5336inputs+0outputs (12major+13985minor)pagefaults 0swaps

so there's a _huge_ increase in system time (again), but the change from 
33% CPU -> 405% CPU makes up for it and you get lower elapsed times.

But that 7x increase in system time really is sad. I do suspect it's 
likely due to spinning on the BKL. And if so, then a modern kernel should 
fix it.

			Linus

  reply	other threads:[~2009-05-08 21:52 UTC|newest]

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-05-07 17:01 (unknown), Bevan Watkiss
2009-05-07 17:13 ` Alex Riesen
2009-05-07 17:26   ` Bevan Watkiss
2009-05-07 18:18     ` Alex Riesen
2009-05-07 18:48       ` Bevan Watkiss
2009-05-07 19:56         ` Björn Steinbrink
2009-05-07 18:56     ` Linus Torvalds
2009-05-07 19:37       ` RE: Bevan Watkiss
2009-05-07 20:07         ` RE: Linus Torvalds
2009-05-07 20:20           ` RE: Linus Torvalds
2009-05-07 20:43             ` Junio C Hamano
2009-05-07 21:33               ` Re: Linus Torvalds
2009-05-07 21:55             ` Linus Torvalds
2009-05-07 22:27               ` RE: david
2009-05-07 22:36                 ` RE: Linus Torvalds
2009-05-07 22:43                   ` RE: david
2009-05-07 23:00                     ` RE: Linus Torvalds
2009-05-07 23:07                       ` RE: david
2009-05-07 23:18                         ` RE: Linus Torvalds
2009-05-07 23:31                           ` RE: david
2009-05-07 23:57                             ` Johan Herland
2009-05-08 16:14                             ` Bevan Watkiss
2009-05-08  8:17               ` Alex Riesen
2009-05-08 14:39                 ` Re: Linus Torvalds
2009-05-08 15:51                   ` Re: Brandon Casey
2009-05-08 16:15                     ` Re: Linus Torvalds
2009-05-08 17:27                       ` Re: Brandon Casey
2009-05-08 17:43                         ` Re: Brandon Casey
2009-05-08 21:49                           ` Linus Torvalds [this message]
2009-05-08 23:04                             ` Re: Brandon Casey
2009-05-09 16:44                               ` Re: Linus Torvalds
2009-05-08 17:44                         ` Re: Linus Torvalds
2009-05-08 16:47               ` 'git checkout' and unlink() calls (was: Re: ) Kjetil Barvik
2009-05-08 17:57                 ` Linus Torvalds
     [not found] <20220301070226.2477769-1-jaydeepjd.8914>
2022-03-06 11:10 ` Jaydeep P Das
2022-03-06 11:22   ` Jaydeep Das
  -- strict thread matches above, loose matches on Subject: below --
2021-08-21 14:40 TECOB270_Ganesh Pawar
2021-08-21 23:52 ` Jeff King
2019-11-15 16:03 Martin Nicolay
2019-11-15 16:29 ` Martin Ågren
2019-11-15 16:37   ` Re: Martin Ågren
2019-08-20 17:23 William Baker
2019-08-20 17:27 ` Yagnatinsky, Mark
2019-03-05 14:57 [GSoC][PATCH v2 3/3] t3600: use helpers to replace test -d/f/e/s <path> Eric Sunshine
2019-03-05 23:38 ` Rohit Ashiwal
2019-01-23 10:50 Christopher Hagler
2019-01-23 14:16 ` Cody Kratzer
2019-01-23 14:25   ` Re: Thomas Braun
2019-01-23 16:00   ` Re: Christopher Hagler
2019-01-23 16:35     ` Randall S. Becker
2019-01-24 17:11   ` Johannes Schindelin
2018-10-08 13:33 Netravnen
2018-10-08 13:34 ` Inderpreet Saini
2018-04-27  0:54 [PATCH v3 2/3] merge: Add merge.renames config setting Ben Peart
2018-04-27 18:19 ` Elijah Newren
2018-04-30 13:11   ` Ben Peart
2018-04-30 16:12     ` Re: Elijah Newren
2018-05-02 14:33       ` Re: Ben Peart
2018-02-27  1:18 Alan Gage
2018-02-27 10:26 ` René Scharfe
2017-11-20 15:10 Viet Nguyen
2017-11-20 20:07 ` Stefan Beller
2017-11-12  2:21 hsed
2017-11-13 18:56 ` Stefan Beller
2017-01-25  0:11 [PATCH 7/7] completion: recognize more long-options Cornelius Weig
2017-01-25  0:21 ` Stefan Beller
2017-01-25  0:43   ` Cornelius Weig
2017-01-25  0:52     ` Re: Stefan Beller
2017-01-25  0:54   ` Re: Linus Torvalds
2017-01-25  1:32     ` Re: Eric Wong
2016-04-11 19:04 (unknown), miwilliams
2016-04-12  4:33 ` Stefan Beller
2015-08-19 19:41 Re: christain147
2015-08-19 11:09 Re: christain147
2015-08-05 12:47 (unknown) Ivan Chernyavsky
2015-08-15  9:19 ` Duy Nguyen
2015-08-17 17:49   ` Re: Junio C Hamano
2015-04-08 20:44 (unknown), Mamta Upadhyay
2015-04-08 21:58 ` Thomas Braun
2015-04-09 11:27   ` Re: Konstantin Khomoutov
     [not found] <CANSxx61FaNp5SBXJ8Y+pWn0eDcunmibKR5g8rttnWGdGwEMHCA@mail.gmail.com>
2015-03-18 20:45 ` Re: Junio C Hamano
2015-03-18 21:06   ` Re: Stefan Beller
2015-03-18 21:17     ` Re: Jeff King
2015-03-18 21:28       ` Re: Jeff King
2015-03-18 21:33         ` Re: Junio C Hamano
2015-03-18 21:45           ` Re: Stefan Beller
2015-03-13  1:34 (unknown) cody.taylor
2015-03-13  2:00 ` Duy Nguyen
2014-09-08 11:36 (unknown), R. Klomp
     [not found] ` <CAOqJoqGSRUw_UT4LhqpYX-WX6AEd2ReAWjgNS76Cra-SMKw3NQ@mail.gmail.com>
2014-09-08 14:36   ` R. Klomp
2014-09-10  0:00     ` Re: David Aguilar
2014-09-15 15:10       ` Re: R. Klomp
2014-02-06 11:54 "Sparse checkout leaves no entry on working directory" all the time on Windows 7 on Git 1.8.5.2.msysgit.0 konstunn
2014-02-06 13:20 ` Johannes Sixt
2014-02-06 19:56   ` Constantine Gorbunov
2012-06-12 21:12 (unknown), rohit sood
2012-06-12 23:51 ` Erik Faye-Lund
2009-11-18  5:03 Re: Anna
2009-05-11 18:57 (unknown) Don Slutz
2009-05-11 20:48 ` Johannes Schindelin
2009-05-12 12:45   ` Re: Don Slutz
2009-03-30  5:03 (unknown), David Aguilar
2009-03-30  7:02 ` Markus Heidelberg
2009-03-30  8:46   ` Re: Junio C Hamano
2007-11-01 20:44 (unknown), Francesco Pretto
2007-11-01 20:48 ` Francesco Pretto
2006-02-02  0:39 [RFC & PATCH] Solaris 8: ENOSYS when mkdir applied to automount., Jason Riedy
2006-02-02  4:18 ` H. Peter Anvin
2005-04-22 22:19 (unknown), atani
2005-04-22 23:16 ` Martin Schlemmer

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