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    SubjectRe: 2.5.2-pre performance degradation on an old 486 (it's the scheduler)
    On Sat, 5 Jan 2002, Mikael Pettersson wrote:

    > On Sat, 5 Jan 2002 09:25:48 +0100 (CET), Matthias Hanisch wrote:
    > >On Sat, 5 Jan 2002, Mikael Pettersson wrote:
    > >
    > >> When running 2.5.2-pre7 on my old for-testing-only 486(*),
    > >> file-system accesses seem to come in distinct bursts preceded
    > >> by lengthy pauses. Overall performance is down quite significantly
    > >> compared to 2.4.18pre1 and 2.2.20pre2. To measure it I ran two
    > >> simple tests:
    > >>
    > >> Test 1: time to boot the kernel, from hitting enter at the LILO
    > >> prompt to getting a login prompt
    > >> Test 2: time to "rm -rf" a clean linux-2.4.17 source tree, using
    > >> the newly booted kernel (no other access to the tree before that,
    > >> so it wasn't cached in any way, and the machine was otherwise idle)
    > >>
    > >> Test 1 Test 2
    > >> 2.2.21pre2: 71 sec 75 sec
    > >> 2.4.18pre1: 64 sec 72 sec
    > >> 2.5.2-pre7: 97 sec 251 sec
    > >>
    > >> I haven't noticed any slowdowns on my other boxes, so I didn't
    > >> do any measurements on them. On the 486 it's very very obvious.
    > >
    > >This is exactly, what I see with my old 486 box. It started with
    > >2.5.2-pre3, which contained two major items:
    > >
    > >- bio changes from Jens
    > >- scheduler changes from Davide
    > >
    > >Surprisingly, backing out the bio changes didn't help. Backing out the
    > >scheduler changes from Davide did!!
    >
    > BINGO! Running 2.5.2-pre8 with the scheduler changes backed out made
    > all the difference! Interactive responsiveness is much improved and
    > performance in the above two tests I ran is back to 2.4.18pre1 levels.
    >
    > With 2.5.2-pre8 vanilla the 486 is getting large variation in Test 2
    > above (157s, 237s, 292s), but is never even close to 2.2/2.4 levels.
    >
    > >> (*) 100MHz 486DX4, 28MB ram, no L2 cache, two old and slow IDE disks,
    > >> small custom no-nonsense RedHat 7.2, kernels compiled with gcc 2.95.3.

    Are you able to profile the kernel ?




    - Davide


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