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    SubjectRe: [PATCH v9 4/7] rcu/trace: Add tracing for how segcb list changes
    On Tue, Nov 03, 2020 at 09:26:00AM -0500, Joel Fernandes (Google) wrote:
    > +/*
    > + * Return how many CBs each segment along with their gp_seq values.
    > + *
    > + * This function is O(N) where N is the number of segments. Only used from
    > + * tracing code which is usually disabled in production.
    > + */
    > +#ifdef CONFIG_RCU_TRACE
    > +static void rcu_segcblist_countseq(struct rcu_segcblist *rsclp,
    > + int cbcount[RCU_CBLIST_NSEGS],
    > + unsigned long gpseq[RCU_CBLIST_NSEGS])
    > +{
    > + int i;
    > +
    > + for (i = 0; i < RCU_CBLIST_NSEGS; i++) {
    > + cbcount[i] = rcu_segcblist_get_seglen(rsclp, i);
    > + gpseq[i] = rsclp->gp_seq[i];
    > + }
    > +}
    > +
    > +void __trace_rcu_segcb_stats(struct rcu_segcblist *rsclp, const char *context)
    > +{
    > + int cbs[RCU_CBLIST_NSEGS];
    > + unsigned long gps[RCU_CBLIST_NSEGS];
    > +
    > + if (!trace_rcu_segcb_stats_enabled())
    > + return;

    Yes, very good!

    Paul just told me that RCU_TRACE can be used in production so that confirms that we
    wanted to avoid this loop of 8 iterations when tracing is disabled.

    Thanks.

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