GFS2: Use average srttb value in congestion calculations

This patch changes function gfs2_rgrp_congested so that it uses an
average srttb (smoothed round trip time for blocking rgrp glocks)
rather than the CPU-specific value. If we use the CPU-specific value
it can incorrectly report no contention when there really is contention
due to the glock processing occurring on a different CPU.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Acked-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 6af2396a317c3de22e9d8bd86e28246b28067523..f39eedc1af7628240925a398dca87069bc294972 100644 (file)
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -1850,14 +1850,19 @@ static bool gfs2_rgrp_congested(const struct gfs2_rgrpd *rgd, int loops)
        const struct gfs2_sbd *sdp = gl->gl_sbd;
        struct gfs2_lkstats *st;
        s64 r_dcount, l_dcount;
-       s64 r_srttb, l_srttb;
+       s64 l_srttb, a_srttb = 0;
        s64 srttb_diff;
        s64 sqr_diff;
        s64 var;
+       int cpu;
 
        preempt_disable();
+       for_each_present_cpu(cpu) {
+               st = &per_cpu_ptr(sdp->sd_lkstats, cpu)->lkstats[LM_TYPE_RGRP];
+               a_srttb += st->stats[GFS2_LKS_SRTTB];
+       }
        st = &this_cpu_ptr(sdp->sd_lkstats)->lkstats[LM_TYPE_RGRP];
-       r_srttb = st->stats[GFS2_LKS_SRTTB];
+       a_srttb /= num_present_cpus();
        r_dcount = st->stats[GFS2_LKS_DCOUNT];
        var = st->stats[GFS2_LKS_SRTTVARB] +
              gl->gl_stats.stats[GFS2_LKS_SRTTVARB];
@@ -1866,10 +1871,10 @@ static bool gfs2_rgrp_congested(const struct gfs2_rgrpd *rgd, int loops)
        l_srttb = gl->gl_stats.stats[GFS2_LKS_SRTTB];
        l_dcount = gl->gl_stats.stats[GFS2_LKS_DCOUNT];
 
-       if ((l_dcount < 1) || (r_dcount < 1) || (r_srttb == 0))
+       if ((l_dcount < 1) || (r_dcount < 1) || (a_srttb == 0))
                return false;
 
-       srttb_diff = r_srttb - l_srttb;
+       srttb_diff = a_srttb - l_srttb;
        sqr_diff = srttb_diff * srttb_diff;
 
        var *= 2;