Re: [PATCH] 2.6.0 - Watchdog patches (BK consistency checks)

From: Ed Tomlinson (edt_at_aei.ca)
Date: 12/31/03

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    To: linux-kernel@vger.kernel.org
Date:	Wed, 31 Dec 2003 11:33:58 -0500

    On December 30, 2003 03:16 pm, Andy Isaacson wrote:
    > On Tue, Dec 30, 2003 at 12:56:32PM -0700, Eric D. Mudama wrote:
    > > On Tue, Dec 30 at 13:13, Andy Isaacson wrote:
    > > >On Tue, Dec 30, 2003 at 08:36:15AM -0500, Ed Tomlinson wrote:
    > > >The consistency check definitely should not take 15 minutes. It should
    > > >be (much) less than 30 seconds. What is the hardware you're running on?
    > > >
    > > >I'm running on an Athlon 2 GHz (XP 2400+) with 512MB and a 7200RPM IDE
    > > >disk, and I can do a complete clone (with full data copy and consistency
    > > >check) of the 2.4 tree in 1:40. That was with cold caches; with the
    > > >sfile copies and "checkout:get", a half-gig isn't enough to cache
    > > >everything. The consistency check is about 19 seconds (bk -r check
    > > > -acv).
    > >
    > > For what it is worth:
    > >
    > > AMD Duron 950MHz, 768MB RAM
    > > 7200RPM 80GB Quantum Viper IDE drive, 26% full
    > >
    > > phat-penguin:~/src/linux-2.5> time bk -r check -acv
    > > 100% |=================================================================|
    > > OK 42.710u 5.770s 2:04.63 38.8% 0+0k 0+0io 74078pf+0w
    > >
    > > over 2 minutes of wall time, 42 seconds of "user" time... (if I'm reading
    > > it right), without primed disk caches.
    > >
    > > The 2nd run, half a minute later:
    > >
    > > phat-penguin:~/src/linux-2.5> time bk -r check -acv
    > > 100% |=================================================================|
    > > OK 41.900u 3.080s 0:45.53 98.7% 0+0k 0+0io 74078pf+0w
    > >
    > >
    > > ...would appear to show that BK's checksumming, on my system, is
    > > constrained near 41 seconds of calculation time, and the difference
    > > between the user and the wall-clock time is basically time spent
    > > waiting for the disk to do all its reads.
    > >
    > >
    > > I guess in that case, it'd be interesting to see what the user and
    > > wall times were for the original poster who reported a 15+ minute
    > > integrity check.
    >
    > That's basically right, except that if you don't have enough memory to
    > keep bk's working set in memory, then you're paging and performance
    > starts to suck.
    >
    > I didn't realize that the cpu-bound portion of the check would scale so
    > closely with CPU speed, but it looks like the scaling is almost dead-on;
    > 18.4/41.9 = .439
    > 950/2000 = .475
    >
    > So I was wrong to say "less than 30 seconds". "If you have a fast CPU
    > and enough memory", I guess. But the memory matters a lot more than the
    > CPU.

    Here are the numbers from my box:

    oscar% cd /usr/src/linux
    oscar% time bk -r check -acv
    100% |=================================================================| OK
    bk -r check -acv 80.63s user 16.18s system 21% cpu 7:32.06 total

    oscar% time bk clone -ql linux yy
    bk clone -ql linux yy 77.57s user 23.49s system 17% cpu 9:50.51 total

    Ed

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