xserver/hw/dmx/dmxsync.c

/*
 * Copyright 2002-2004 Red Hat Inc., Durham, North Carolina.
 *
 * All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation on the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NON-INFRINGEMENT.  IN NO EVENT SHALL RED HAT AND/OR THEIR SUPPLIERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/*
 * Authors:
 *   Rickard E. (Rik) Faith <faith@redhat.com>
 *
 */

/** \file
 *
 * The DMX server code is written to call #dmxSync() whenever an XSync()
 * might be necessary.  However, since XSync() requires a two way
 * communication with the other X server, eliminating unnecessary
 * XSync() calls is a key performance optimization.  Support for this
 * optimization is provided here.  Statistics about XSync() calls and
 * latency are gathered in \a dmxstat.c.
 *
 * During the initial conversion from calling XSync() immediately to the
 * XSync() batching method implemented in this file, it was noted that,
 * out of more than 300 \a x11perf tests, 8 tests became more than 100
 * times faster, with 68 more than 50X faster, 114 more than 10X faster,
 * and 181 more than 2X faster. */

#ifdef HAVE_DMX_CONFIG_H
#include <dmx-config.h>
#endif

#include "dmx.h"
#include "dmxsync.h"
#include "dmxstat.h"
#include "dmxlog.h"
#include <sys/time.h>

static int dmxSyncInterval = 100;       /* Default interval in milliseconds */
static OsTimerPtr dmxSyncTimer;
static int dmxSyncPending;

static void
dmxDoSync(DMXScreenInfo * dmxScreen)
{
    dmxScreen->needsSync = FALSE;

    if (!dmxScreen->beDisplay)
        return;                 /* FIXME: Is this correct behavior for sync stats? */

    if (!dmxStatInterval) {
        XSync(dmxScreen->beDisplay, False);
    }
    else {
        struct timeval start, stop;

        gettimeofday(&start, 0);
        XSync(dmxScreen->beDisplay, False);
        gettimeofday(&stop, 0);
        dmxStatSync(dmxScreen, &stop, &start, dmxSyncPending);
    }
}

static CARD32
dmxSyncCallback(OsTimerPtr timer, CARD32 time, void *arg)
{
    int i;

    if (dmxSyncPending) {
        for (i = 0; i < dmxNumScreens; i++) {
            DMXScreenInfo *dmxScreen = &dmxScreens[i];

            if (dmxScreen->needsSync)
                dmxDoSync(dmxScreen);
        }
    }
    dmxSyncPending = 0;
    return 0;                   /* Do not place on queue again */
}

static void
dmxSyncBlockHandler(void *blockData, void *timeout)
{
    TimerForce(dmxSyncTimer);
}

static void
dmxSyncWakeupHandler(void *blockData, int result)
{
}

/** Request the XSync() batching optimization with the specified \a
 * interval (in mS).  If the \a interval is 0, 100mS is used.  If the \a
 * interval is less than 0, then the XSync() batching optimization is
 * not requested (e.g., so the -syncbatch -1 command line option can
 * turn off the default 100mS XSync() batching).
 *
 * Note that the parameter to this routine is a string, since it will
 * usually be called from #ddxProcessArgument in \a dmxinit.c */
void
dmxSyncActivate(const char *interval)
{
    dmxSyncInterval = (interval ? atoi(interval) : 100);

    if (dmxSyncInterval < 0)
        dmxSyncInterval = 0;
}

/** Initialize the XSync() batching optimization, but only if
 * #dmxSyncActivate was last called with a non-negative value. */
void
dmxSyncInit(void)
{
    if (dmxSyncInterval) {
        RegisterBlockAndWakeupHandlers(dmxSyncBlockHandler,
                                       dmxSyncWakeupHandler, NULL);
        dmxLog(dmxInfo, "XSync batching with %d ms interval\n",
               dmxSyncInterval);
    }
    else {
        dmxLog(dmxInfo, "XSync batching disabled\n");
    }
}

/** Request an XSync() to the display used by \a dmxScreen.  If \a now
 * is TRUE, call XSync() immediately instead of waiting for the next
 * XSync() batching point.  Note that if XSync() batching was deselected
 * with #dmxSyncActivate() before #dmxSyncInit() was called, then no
 * XSync() batching is performed and this function always calls XSync()
 * immediately.
 *
 * (Note that this function uses TimerSet but works correctly in the
 * face of a server generation.  See the source for details.)
 *
 * If \a dmxScreen is \a NULL, then all pending syncs will be flushed
 * immediately.
 */
void
dmxSync(DMXScreenInfo * dmxScreen, Bool now)
{
    static unsigned long dmxGeneration = 0;

    if (dmxSyncInterval) {
        if (dmxGeneration != serverGeneration) {
            /* Server generation does a TimerInit, which frees all
             * timers.  So, at this point dmxSyncTimer is either:
             * 1) NULL, iff dmxGeneration == 0,
             * 2) freed, if it was on a queue (dmxSyncPending != 0), or
             * 3) allocated, if it wasn't on a queue (dmxSyncPending == 0)
             */
            if (dmxSyncTimer && !dmxSyncPending)
                free(dmxSyncTimer);
            dmxSyncTimer = NULL;
            now = TRUE;
            dmxGeneration = serverGeneration;
        }
        /* Queue sync */
        if (dmxScreen) {
            dmxScreen->needsSync = TRUE;
            ++dmxSyncPending;
        }

        /* Do sync or set time for later */
        if (now || !dmxScreen) {
            if (dmxSyncTimer == NULL || !TimerForce(dmxSyncTimer))
                dmxSyncCallback(NULL, 0, NULL);
            /* At this point, dmxSyncPending == 0 because
             * dmxSyncCallback must have been called. */
            if (dmxSyncPending)
                dmxLog(dmxFatal, "dmxSync(%s,%d): dmxSyncPending = %d\n",
                       dmxScreen ? dmxScreen->name : "", now, dmxSyncPending);
        }
        else {
            dmxScreen->needsSync = TRUE;
            if (dmxSyncPending == 1)
                dmxSyncTimer = TimerSet(dmxSyncTimer, 0, dmxSyncInterval,
                                        dmxSyncCallback, NULL);
        }
    }
    else {
        /* If dmxSyncInterval is not being used,
         * then all the backends are already
         * up-to-date. */
        if (dmxScreen)
            dmxDoSync(dmxScreen);
    }
}