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    SubjectRe: [PATCH 00/13] blk-throttle: lockless bio processing for no throttle rule group [V2]
    On Thu, May 19, 2011 at 03:38:18PM -0400, Vivek Goyal wrote:
    > Hi,
    > This is V2 of the patch. Changes from V1 are.
    > - Dropped first patch of the series which has already been merged.
    > - Fixed couple of white space warnings.
    > Jens, I am sending this series on your both the ids. See if both produce
    > warnings.
    > Block throttling code takes request queue lock for every incoming bio
    > (blk_throtl_bio()). This is true even if there are no throttle rules in
    > the group. This is a common case for root cgroup where distributions
    > will have throttling support compiled in but a vast majority of users
    > will not be specifying throttling rule.
    > This patch series tries to make bio processing lockless (no requeust
    > queue lock), if there are no rules specified for the group. Once
    > a bio is submitted, under rcu_read_lock() we search for the group,
    > update the stats and release the rcu lock. request queue lock is taken
    > only if there are throttling rules specified in the group.
    > I have made some of the dispatch stats per cpu so that these can be updated
    > without taking request queue lock.

    Also forgot to mention that now throttling path does not take blkg->stat_lock
    at all. Throttling updates only 3 stats and all these 3 stats have been
    converted to per cpu, hence we got rid of the need of taking blkg->stat_lock

    Divyesh, can you have a look at locking changes around stats and see if
    you have any concerns.


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