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    SubjectRe: Ctrl+C doesn't interrupt process waiting for I/O
    Jeremy Fitzhardinge wrote:
    > Török Edwin wrote:
    >> Hi,
    >> I have encountered the following situation several times, but I've been
    >> unable to come up with a way to reproduce this until now:
    >> - some process is keeping the disk busy (some cron job for example:
    >> updatedb, chkrootkit, ...)
    >> - other processes that want to do I/O have to wait (this is normal)
    >> - I have a (I/O bound) process running in my terminal, and I want to
    >> interrupt it with Ctrl+C
    >> - I type Ctrl+C several times, and the process is not interrupted for
    >> several seconds (10-30 secs)
    >> - if I type Ctrl+Z, and use kill %1 the process dies faster than
    >> waiting for it to react to Ctrl+C
    >> This issue occurs both on my x86-64 machine that uses reiserfs, and on
    >> my x86 machine that uses XFS, so it doesn't seem related to the
    >> underlying FS.
    >> I use 2.6.25-2 and 2.6.26-rc8 now; I don't recall seeing this behaviour
    >> with old kernels (IIRC I see this since 2.6.21 or 2.6.23).
    >> Is this intended behaviour, or should I report a bug?
    > Yes, it's intended behaviour. Filesystem IO syscalls are considered
    > "fast" and are interruptible. Usermode code can reasonably expect
    > that file IO will never return EINTR.


    > That said, if a program is blocking for tens of seconds in block IO,
    > then that could be a problem in itself.

    In that case I don't think that a program doing heavy I/O (writeout of
    100Mb+) should be able to block other processes waiting for I/O on the
    same device for tens of seconds.
    I am using CFQ as I/O scheduler now, I will try the other I/O schedulers
    (especially deadline) and see if I get better behaviour.

    Is there any documentation on the tunable values for CFQ? (in
    Documentation/block there is only about anticipatory and deadline).

    Best regards,

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