root/trunk/varnish-cache/bin/varnishd/mgt_pool.c @ 4599

/*-
 * Copyright (c) 2006 Verdens Gang AS
 * Copyright (c) 2006-2009 Linpro AS
 * All rights reserved.
 *
 * Author: Poul-Henning Kamp <phk@phk.freebsd.dk>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * We maintain a number of worker thread pools, to spread lock contention.
 *
 * Pools can be added on the fly, as a means to mitigate lock contention,
 * but can only be removed again by a restart. (XXX: we could fix that)
 *
 * Two threads herd the pools, one eliminates idle threads and aggregates
 * statistics for all the pools, the other thread creates new threads
 * on demand, subject to various numerical constraints.
 *
 * The algorithm for when to create threads needs to be reactive enough
 * to handle startup spikes, but sufficiently attenuated to not cause
 * thread pileups.  This remains subject for improvement.
 */

#include "config.h"

#include "svnid.h"
SVNID("$Id$")
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>
#include <sys/types.h>

#include "cli_priv.h"
#include "mgt.h"

#include "vparam.h"
#include "heritage.h"

/*--------------------------------------------------------------------*/

static void
tweak_thread_pool_min(struct cli *cli, const struct parspec *par,
    const char *arg)
{

        tweak_generic_uint(cli, &master.wthread_min, arg,
            (unsigned)par->min, master.wthread_max);
}

/*--------------------------------------------------------------------
 * This is utterly ridiculous:  POSIX does not guarantee that the 
 * minimum thread stack size is a compile time constant.
 * XXX: "32" is a magic marker for 32bit systems.
 */

static void
tweak_stack_size(struct cli *cli, const struct parspec *par,
    const char *arg)
{
        unsigned low, u;
        char buf[12];

        low = sysconf(_SC_THREAD_STACK_MIN);

        if (arg != NULL && !strcmp(arg, "32")) {
                u = 65536;
                if (u < low)
                        u = low;
                sprintf(buf, "%u", u);
                arg = buf;
        }

        tweak_generic_uint(cli, &master.wthread_stacksize, arg,
            low, (uint)par->max);
}

/*--------------------------------------------------------------------*/

static void
tweak_thread_pool_max(struct cli *cli, const struct parspec *par,
    const char *arg)
{

        (void)par;
        tweak_generic_uint(cli, &master.wthread_max, arg,
            master.wthread_min, UINT_MAX);
}

/*--------------------------------------------------------------------*/

const struct parspec WRK_parspec[] = {
        { "thread_pools", tweak_uint, &master.wthread_pools, 1, UINT_MAX,
                "Number of worker thread pools.\n"
                "\n"
                "Increasing number of worker pools decreases lock "
                "contention.\n"
                "\n"
                "Too many pools waste CPU and RAM resources, and more than "
                "one pool for each CPU is probably detrimal to performance.\n"
                "\n"
                "Can be increased on the fly, but decreases require a "
                "restart to take effect.",
                EXPERIMENTAL | DELAYED_EFFECT,
                "2", "pools" },
        { "thread_pool_max", tweak_thread_pool_max, NULL, 1, 0,
                "The maximum number of worker threads in all pools combined.\n"
                "\n"
                "Do not set this higher than you have to, since excess "
                "worker threads soak up RAM and CPU and generally just get "
                "in the way of getting work done.\n",
                EXPERIMENTAL | DELAYED_EFFECT,
                "500", "threads" },
        { "thread_pool_min", tweak_thread_pool_min, NULL, 2, 0,
                "The minimum number of threads in each worker pool.\n"
                "\n"
                "Increasing this may help ramp up faster from low load "
                "situations where threads have expired.\n"
                "\n"
                "Minimum is 2 threads.",
                EXPERIMENTAL | DELAYED_EFFECT,
                "5", "threads" },
        { "thread_pool_timeout", tweak_timeout, &master.wthread_timeout, 1, 0,
                "Thread idle threshold.\n"
                "\n"
                "Threads in excess of thread_pool_min, which have been idle "
                "for at least this long are candidates for purging.\n"
                "\n"
                "Minimum is 1 second.",
                EXPERIMENTAL | DELAYED_EFFECT,
                "300", "seconds" },
        { "thread_pool_purge_delay",
                tweak_timeout, &master.wthread_purge_delay, 100, 0,
                "Wait this long between purging threads.\n"
                "\n"
                "This controls the decay of thread pools when idle(-ish).\n"
                "\n"
                "Minimum is 100 milliseconds.",
                EXPERIMENTAL | DELAYED_EFFECT,
                "1000", "milliseconds" },
        { "thread_pool_add_threshold",
                tweak_uint, &master.wthread_add_threshold, 0, UINT_MAX,
                "Overflow threshold for worker thread creation.\n"
                "\n"
                "Setting this too low, will result in excess worker threads, "
                "which is generally a bad idea.\n"
                "\n"
                "Setting it too high results in insuffient worker threads.\n",
                EXPERIMENTAL,
                "2", "requests" },
        { "thread_pool_add_delay",
                tweak_timeout, &master.wthread_add_delay, 0, UINT_MAX,
                "Wait at least this long between creating threads.\n"
                "\n"
                "Setting this too long results in insuffient worker threads.\n"
                "\n"
                "Setting this too short increases the risk of worker "
                "thread pile-up.\n",
                EXPERIMENTAL,
                "20", "milliseconds" },
        { "thread_pool_fail_delay",
                tweak_timeout, &master.wthread_fail_delay, 100, UINT_MAX,
                "Wait at least this long after a failed thread creation "
                "before trying to create another thread.\n"
                "\n"
                "Failure to create a worker thread is often a sign that "
                " the end is near, because the process is running out of "
                "RAM resources for thread stacks.\n"
                "This delay tries to not rush it on needlessly.\n"
                "\n"
                "If thread creation failures are a problem, check that "
                "thread_pool_max is not too high.\n"
                "\n"
                "It may also help to increase thread_pool_timeout and "
                "thread_pool_min, to reduce the rate at which treads are "
                "destroyed and later recreated.\n",
                EXPERIMENTAL,
                "200", "milliseconds" },
        { "thread_stats_rate",
                tweak_uint, &master.wthread_stats_rate, 0, UINT_MAX,
                "Worker threads accumulate statistics, and dump these into "
                "the global stats counters if the lock is free when they "
                "finish a request.\n"
                "This parameters defines the maximum number of requests "
                "a worker thread may handle, before it is forced to dump "
                "its accumulated stats into the global counters.\n",
                EXPERIMENTAL,
                "10", "requests" },
        { "overflow_max", tweak_uint, &master.overflow_max, 0, UINT_MAX,
                "Percentage permitted overflow queue length.\n"
                "\n"
                "This sets the ratio of queued requests to worker threads, "
                "above which sessions will be dropped instead of queued.\n",
                EXPERIMENTAL,
                "100", "%" },
        { "rush_exponent", tweak_uint, &master.rush_exponent, 2, UINT_MAX,
                "How many parked request we start for each completed "
                "request on the object.\n"
                "NB: Even with the implict delay of delivery, "
                "this parameter controls an exponential increase in "
                "number of worker threads.  ",
                EXPERIMENTAL,
                "3", "requests per request" },
        { "thread_pool_stack",
                tweak_stack_size, &master.wthread_stacksize, 0, UINT_MAX,
                "Worker thread stack size.\n"
                "On 32bit systems you may need to tweak this down to fit "
                "many threads into the limited address space.\n",
                EXPERIMENTAL,
                "-1", "bytes" },
        { NULL, NULL, NULL }
};