[MEDIUM] limit the number of events returned by *poll*

By default, epoll/kqueue used to return as many events as possible.
This could sometimes cause huge latencies (latencies of up to 400 ms
have been observed with many thousands of fds at once). Limiting the
number of events returned also reduces the latency by avoiding too
many blind processing. The value is set to 200 by default and can be
changed in the global section using the tune.maxpollevents parameter.

diff --git a/doc/haproxy-en.txt b/doc/haproxy-en.txt
index 865bf8e41ff37e252ae675269c4185f373c1f1c9..73372e367e2e0b13681d460efcd63e88fa13fcf3 100644 (file)
--- a/doc/haproxy-en.txt
+++ b/doc/haproxy-en.txt
@@ -128,6 +128,7 @@ the following ones :
   - pidfile <file>
   - ulimit-n <number>
   - stats
+  - tune.maxpollevents <number>
 
 
 1.1) Event logging
@@ -338,6 +339,12 @@ Tests have shown constant performance from 1 to 20000 simultaneous sessions.
 Version 1.3.9 introduced kqueue() for FreeBSD/OpenBSD, and speculative epoll()
 which consists in trying to perform I/O before queuing the events via syscalls.
 
+In order to optimize latency, it is now possible to limit the number of events
+returned by a single call to poll. The limit is fixed to 200 by default. If a
+smaller latency is seeked, it may be useful to reduce this value by using the
+'tune.maxpollevents' parameter in the 'global' section. Increasing it will
+slightly save CPU cycles in presence of large number of connections.
+
 Haproxy will use kqueue() or speculative epoll() when available, then epoll(),
 and will fall back to poll(), then to select(). However, if for any reason you
 need to disable epoll() or poll() (eg. because of a bug or just to compare
@@ -351,6 +358,7 @@ Example :
         # use only select()
         noepoll
         nopoll
+        tune.maxpollevents 100
 
 Note :
 ------

diff --git a/doc/haproxy-fr.txt b/doc/haproxy-fr.txt
index 63ac9a4514f6e695ea0b39d6335170e7303d2cc2..ec746114962f94ed673d1c98bcfac0a190be6cd3 100644 (file)
--- a/doc/haproxy-fr.txt
+++ b/doc/haproxy-fr.txt
@@ -134,6 +134,7 @@ support
   - quiet
   - pidfile <fichier>
   - ulimit-n <nombre>
+  - tune.maxpollevents <nombre>
 
 
 1.1) Journalisation des événements
@@ -362,6 +363,13 @@ qu'une variante appel
 les opérations d'entrées/sorties avant de chaîner les événements par les appels
 système.
 
+Afin d'optimiser la latence, il est désormais possible de limiter le nombre
+d'événements remontés à chaque appel. La limite par défaut est fixée à 200. Si
+une latence plus petite est recherchée, il peut être justifié d'abaisser cette
+limite par l'utilisation du paramètre 'tune.maxpollevents' dans la section
+'global'. L'augmenter permettra d'économiser un peu le processeur en présence
+de très grands nombres de connexions simultanées.
+
 Haproxy utilisera kqueue() ou speculative epoll() lorsque ce sera disponible,
 puis epoll(), et se repliera sur poll(), puis en dernier lieu sur select().
 Cependant, si pour une raison quelconque il s'avérait nécessaire de désactiver
@@ -375,6 +383,7 @@ Exemple :
         # utiliser seulement select()
         noepoll
         nopoll
+        tune.maxpollevents 100
 
 Remarque :
 ----------

diff --git a/include/common/defaults.h b/include/common/defaults.h
index cfe60e8f9cc24794aa4f284bcac299c489cf8c16..198288fb9a9651289b52df1e1771a4cf4efe058c 100644 (file)
--- a/include/common/defaults.h
+++ b/include/common/defaults.h
@@ -2,7 +2,7 @@
   include/common/defaults.h
   Miscellaneous default values.
 
-  Copyright (C) 2000-2006 Willy Tarreau - w@1wt.eu
+  Copyright (C) 2000-2007 Willy Tarreau - w@1wt.eu
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
@@ -78,6 +78,12 @@
 #define MIN_RET_FOR_READ_LOOP 1460
 #endif
 
+// the max number of events returned in one call to poll/epoll. Too small a
+// value will cause lots of calls, and too high a value may cause high latency.
+#ifndef MAX_POLL_EVENTS
+#define MAX_POLL_EVENTS 200
+#endif
+
 // cookie delimitor in "prefix" mode. This character is inserted between the
 // persistence cookie and the original value. The '~' is allowed by RFC2965,
 // and should not be too common in server names.

diff --git a/include/types/global.h b/include/types/global.h
index 222d4feacd548e7011b6686a73f1104b99dfc536..b25995491ec132adf5dd345e882eb1ed375cf443 100644 (file)
--- a/include/types/global.h
+++ b/include/types/global.h
@@ -60,6 +60,9 @@ struct global {
        int logfac1, logfac2;
        int loglev1, loglev2;
        struct sockaddr_in logsrv1, logsrv2;
+       struct {
+               int maxpollevents; /* max number of poll events at once */
+       } tune;
 };
 
 extern struct global global;

diff --git a/src/cfgparse.c b/src/cfgparse.c
index 5045ed27f94c320053121c4d1c0764a3b21a41b7..69f11e0c53b8e4d6bf33453c97c99332e25c5c24 100644 (file)
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -276,6 +276,17 @@ int cfg_parse_global(const char *file, int linenum, char **args)
        else if (!strcmp(args[0], "stats")) {
                global.mode |= MODE_STATS;
        }
+       else if (!strcmp(args[0], "tune.maxpollevents")) {
+               if (global.tune.maxpollevents != 0) {
+                       Alert("parsing [%s:%d] : '%s' already specified. Continuing.\n", file, linenum, args[0]);
+                       return 0;
+               }
+               if (*(args[1]) == 0) {
+                       Alert("parsing [%s:%d] : '%s' expects an integer argument.\n", file, linenum, args[0]);
+                       return -1;
+               }
+               global.tune.maxpollevents = atol(args[1]);
+       }
        else if (!strcmp(args[0], "uid")) {
                if (global.uid != 0) {
                        Alert("parsing [%s:%d] : user/uid already specified. Continuing.\n", file, linenum);

diff --git a/src/ev_epoll.c b/src/ev_epoll.c
index 9dccb3526c53271ec0c8f038555dc95e9abeab3f..a0c48b108118a8def0440f277aa08a761b5c69fc 100644 (file)
--- a/src/ev_epoll.c
+++ b/src/ev_epoll.c
@@ -18,6 +18,7 @@
 #include <common/config.h>
 #include <common/standard.h>
 #include <common/time.h>
+#include <common/tools.h>
 
 #include <types/fd.h>
 #include <types/global.h>
@@ -238,7 +239,8 @@ REGPRM2 static void _do_poll(struct poller *p, struct timeval *exp)
        else
                wait_time = __tv_ms_elapsed(&now, exp) + 1;
 
-       status = epoll_wait(epoll_fd, epoll_events, maxfd, wait_time);
+       fd = MIN(maxfd, global.tune.maxpollevents);
+       status = epoll_wait(epoll_fd, epoll_events, fd, wait_time);
        tv_now(&now);
 
        for (count = 0; count < status; count++) {
@@ -278,7 +280,7 @@ REGPRM1 static int _do_init(struct poller *p)
                goto fail_fd;
 
        epoll_events = (struct epoll_event*)
-               calloc(1, sizeof(struct epoll_event) * global.maxsock);
+               calloc(1, sizeof(struct epoll_event) * global.tune.maxpollevents);
 
        if (epoll_events == NULL)
                goto fail_ee;

diff --git a/src/ev_kqueue.c b/src/ev_kqueue.c
index 8740217b854e945e9e763e08dbd07fe97fb8766b..773db74a3bfa8dd13661b2f00330fce24df46cb6 100644 (file)
--- a/src/ev_kqueue.c
+++ b/src/ev_kqueue.c
@@ -24,6 +24,7 @@
 #include <common/compat.h>
 #include <common/config.h>
 #include <common/time.h>
+#include <common/tools.h>
 
 #include <types/fd.h>
 #include <types/global.h>
@@ -118,11 +119,12 @@ REGPRM2 static void _do_poll(struct poller *p, struct timeval *exp)
                to_ptr = &timeout;
        }
 
+       fd = MIN(maxfd, global.tune.maxpollevents);
        status = kevent(kqueue_fd, // int kq
                        NULL,      // const struct kevent *changelist
                        0,         // int nchanges
                        kev,       // struct kevent *eventlist
-                       maxfd,     // int nevents
+                       fd,        // int nevents
                        to_ptr);   // const struct timespec *timeout
        tv_now(&now);
 
@@ -161,7 +163,7 @@ REGPRM1 static int _do_init(struct poller *p)
        if (kqueue_fd < 0)
                goto fail_fd;
 
-       kev = (struct kevent*)calloc(1, sizeof(struct kevent) * global.maxsock);
+       kev = (struct kevent*)calloc(1, sizeof(struct kevent) * global.tune.maxpollevents);
 
        if (kev == NULL)
                goto fail_kev;

diff --git a/src/ev_sepoll.c b/src/ev_sepoll.c
index d304c12900a25916be0b087548b8c6b1736ec2db..852577caa6e5837ed3917e1036e6eab9d752770e 100644 (file)
--- a/src/ev_sepoll.c
+++ b/src/ev_sepoll.c
@@ -18,6 +18,7 @@
 #include <common/config.h>
 #include <common/standard.h>
 #include <common/time.h>
+#include <common/tools.h>
 
 #include <types/fd.h>
 #include <types/global.h>
@@ -389,7 +390,8 @@ REGPRM2 static void _do_poll(struct poller *p, struct timeval *exp)
        }
 
        /* now let's wait for real events */
-       status = epoll_wait(epoll_fd, epoll_events, maxfd, wait_time);
+       fd = MIN(maxfd, global.tune.maxpollevents);
+       status = epoll_wait(epoll_fd, epoll_events, fd, wait_time);
 
        tv_now(&now);
 
@@ -439,7 +441,7 @@ REGPRM1 static int _do_init(struct poller *p)
                goto fail_fd;
 
        epoll_events = (struct epoll_event*)
-               calloc(1, sizeof(struct epoll_event) * global.maxsock);
+               calloc(1, sizeof(struct epoll_event) * global.tune.maxpollevents);
 
        if (epoll_events == NULL)
                goto fail_ee;

diff --git a/src/haproxy.c b/src/haproxy.c
index a86abeb3196d3a47f416d05e4d69d030c4ab1470..e0e42b23fccf5400428d226603217482a70a36ad 100644 (file)
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -520,6 +520,9 @@ void init(int argc, char **argv)
 
        global.maxsock += global.maxconn * 2; /* each connection needs two sockets */
 
+       if (global.tune.maxpollevents <= 0)
+               global.tune.maxpollevents = MAX_POLL_EVENTS;
+
        if (arg_mode & (MODE_DEBUG | MODE_FOREGROUND)) {
                /* command line debug mode inhibits configuration mode */
                global.mode &= ~(MODE_DAEMON | MODE_QUIET);