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SubjectRe: [patch 00/17] CFS Bandwidth Control v7.1
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On Thu, 2011-07-07 at 13:23 +0200, Ingo Molnar wrote:
>
> The +1.5% increase in vanilla kernel context switching performance is
> unfortunate - where does that overhead come from?

Looking at the asm output, I think its partly because things like:

@@ -602,6 +618,8 @@ static void update_curr(struct cfs_rq *c
cpuacct_charge(curtask, delta_exec);
account_group_exec_runtime(curtask, delta_exec);
}
+
+ account_cfs_rq_runtime(cfs_rq, delta_exec);
}

+static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
+ unsigned long delta_exec)
+{
+ if (!cfs_rq->runtime_enabled)
+ return;
+
+ cfs_rq->runtime_remaining -= delta_exec;
+ if (cfs_rq->runtime_remaining > 0)
+ return;
+
+ assign_cfs_rq_runtime(cfs_rq);
+}
generate a call, only to then take the first branch out, marking that
function __always_inline would cure the call problem. Going beyond that
would be using static_branch() to track if there is any bandwidth
tracking required at all.


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