[systemd-devel] [PATCH 1/2] RFC: journald: Allow to cache the cg_get_root_path
k.lewandowsk at samsung.com
Thu Jul 18 11:32:18 PDT 2013
On 07/16/2013 03:26 AM, Lennart Poettering wrote:
> On Mon, 08.07.13 18:39, Karol Lewandowski (k.lewandowsk at samsung.com) wrote:
>> According to my analysis /proc access is costly and it would
>> be best to cache the result for later use. Difficulty comes
>> from trying to keep cache up to date, though.
> We can't really cache this. This stuff is already racy, as by the time
> we read the attributes the process might already be gone.
Agreed, this is why I have been naively thinking that caching wouldn't
be that bad... However, sending all the required information in message
itself is clearly the best solution to this problem.
> I think the best way to deal with the performance issue here is the
> stuff discussed here:
> i.e. just have the kernel augment our messages with the data we need,
> unconditionally. That way we fix both the race issue, and the
> performance issue, since the data is just there and we can make use of
> it without any further work.
Thanks a lot for this link!
Having this issue sorted out will allow me to take closer look
into "eliminating" 64-bit divisions in message receive path.
ARM doesn't support divide operation so every div is being
done purely in software.
 Every div/% by non-constant value and every div/% by
64-bit constant results in call to (slow) __aeabi_div*.
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