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Directory lookups show up in profiling. The queue files are responsible
for a large proportion of file-related system calls in udev coldplug.
Instead of creating a file for each event, append their details to a
log file. The file is periodically rebuilt (garbage-collected) to
prevent it from growing indefinitely.
This single queue file replaces both the queue directory and the
uevent_seqnum file. On desktop systems the file tends not to grow
beyond one page. So it should also save a small amount of memory in
tmpfs.
Tests on a running EeePC indicate average savings of 5% *udevd* cpu time
as measured by oprofile. __link_path_walk is reduced from 1.5% to
1.3%. It is not completely clear where the rest of the gains come from.
In tests running ~400 events, the queue file is rebuilt about 5 times.
Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
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On Thu, Apr 23, 2009 at 11:39, Alan Jenkins <alan-jenkins@tuffmail.co.uk> wrote:
> I'm puzzled by this function:
>
> /* if we have not seen this seqnum, check if it is/was already queued */
> if (seqnum < udev_queue->last_seen_udev_seqnum) {
> udev_queue_get_udev_seqnum(udev_queue);
> if (seqnum < udev_queue->last_seen_udev_seqnum)
>
> Shouldn't the test be (seqnum > udev_queue->last_seen_udev_seqnum) ?
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Use calloc to request cleared memory instead.
Kernel and libc conspire to make this more efficient.
Also, replace one malloc() + strcpy() with strdup().
Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
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