[lkml]   [1999]   [Jul]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Scheduling latencies news: less RAM = less latency
    Hi all,

    It was not my profile, I only forwarded it to Benno.
    It was found on the list, as "Excessive System time in MSP kernel."
    And it was run on a 512 MB Dual Pentium(!) system.
    [Note: maximum memory on a (well, two) slow Pentium, but the timing
    for each function should be the same]

    When I reported it I was running in Win95 I could not check out
    man readprofile (and I can not now either...)

    I noted that I was guessing a little but the data did look
    like it was number of calls, label, average time (look at
    total line)... [I am in a process of moving all my lists
    from Win95 to Linux, but I am waiting for my ISP to add
    some mail accounts...]

    I have a patch of my own, not related to data in the above
    thread, that measures the time from setting of
    current->need_resched to the actual (re)scheduling takes place.
    It also samples instruction pointer at jiffies and prints data in
    schedule() if latency is longer than 5 ms (i.e. definable)
    - and that happens a lot!
    [I have kept it private group since it is my first patch and
    I do not think that it is SMP safe... or safe in any other

    And the readprofile from the forwarded thread "matches" the
    data I get...

    There are stuff that takes several jiffies before it
    reschedules... (PPro 180, 96MB)

    Linus Torvalds says later in the tread:
    > Also, the si_meminfo() etc stuff is just ridiculous. It's not a question
    > of latency: it's a question of CPU usage. We need to just get rid of those
    > functions instead of hacking around them - regardless of whether you add
    > "reschedule" calls in them, they just eat too much CPU, plain and simple.
    > Again, please don't treat the symptoms - I will not accept patches that
    > just say "oh, this is crap, so let's reschedule a bit here". They need to
    > be fixed properly or not at all.

    I fully agree!

    But Ingos patches are a nice start - they show that it can be done!


    Benno Senoner wrote:
    > Hi folks, again news
    > as Roger Larrson suspected, there are some parts in the kernel
    > which have a too long execution path:
    > On his PPro with 512MB RAM, d_lookup takes up to 80ms to execute !
    > (I put Roger's latency profiling patch on my page)


    The Internet interprets Windows as damage,
    and routes around it.

    Roger Larsson

    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:53    [W:0.039 / U:70.568 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site