Optimize shmlog writing:

If we know the record length, only hold the mutex while we reserve
the space.  Until we change the first byte, nothing bad can happen.

XXX: a memory barrier is strictly speaking necessary before we assign
the first byte.

If there are no '%' in the format string, treat as fixed length for
speed.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@895 d4fa192b-c00b-0410-8231-f00ffab90ce4

diff --git a/varnish-cache/bin/varnishd/shmlog.c b/varnish-cache/bin/varnishd/shmlog.c
index 45339cf3afa642b0f8b8397fea2f5d5c1daa97a3..7db7d48f8c08018cad271ecc894fc6198981b62c 100644 (file)
--- a/varnish-cache/bin/varnishd/shmlog.c
+++ b/varnish-cache/bin/varnishd/shmlog.c
@@ -61,6 +61,7 @@ VSLR(enum shmlogtag tag, unsigned id, const char *b, const char *e)
                e = b + l;
        }
 
+       /* Only hold the lock while we find our space */
        AZ(pthread_mutex_lock(&vsl_mtx));
        assert(loghead->ptr < loghead->size);
 
@@ -68,17 +69,18 @@ VSLR(enum shmlogtag tag, unsigned id, const char *b, const char *e)
        if (loghead->ptr + 5 + l + 1 > loghead->size)
                vsl_wrap();
        p = logstart + loghead->ptr;
+       loghead->ptr += 5 + l;
+       p[5 + l] = SLT_ENDMARKER;
+       assert(loghead->ptr < loghead->size);
+       AZ(pthread_mutex_unlock(&vsl_mtx));
+
        p[1] = l & 0xff;
        p[2] = (id >> 8) & 0xff;
        p[3] = id & 0xff;
        memcpy(p + 4, b, l);
        p[4 + l] = '\0';
-       p[5 + l] = SLT_ENDMARKER;
+       /* XXX: memory barrier */
        p[0] = tag;
-
-       loghead->ptr += 5 + l;
-       assert(loghead->ptr < loghead->size);
-       AZ(pthread_mutex_unlock(&vsl_mtx));
 }
 
 
@@ -91,6 +93,12 @@ VSL(enum shmlogtag tag, unsigned id, const char *fmt, ...)
 
        va_start(ap, fmt);
 
+       p = strchr(fmt, '%');
+       if (p == NULL) {
+               VSLR(tag, id, fmt, NULL);
+               return;
+       }
+
        AZ(pthread_mutex_lock(&vsl_mtx));
        assert(loghead->ptr < loghead->size);