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Commit e43c2483 authored by Brad Fitzpatrick's avatar Brad Fitzpatrick
Browse files

More fixes to Binder perf regression from Eclair 

Re-use the file descriptor to change the cgroups.  There's a fast path
in the kernel for the case where the value's already uncahnged.  Also,
this is okay because the kernel ignores the write offset.  This is
essentially a ioctl-ish/datagram interface, despite being a fd we're
writing to.

This reduces Dalvik->Dalvik void/void Binder calls on Sapphire from
~1.2 to ~0.8 ms.  This is a bit slower than the ~0.7 ms we get
avoiding the write altogether.

strace confirms:

[pid  1557] ioctl(21, 0xc0186201 <unfinished ...>
[pid  1556] <... ioctl resumed> , 0x45399cd0) = 0
[pid  1556] write(22, "1556", 4)        = 4
[pid  1556] ioctl(21, 0xc0186201 <unfinished ...>
[pid  1555] <... ioctl resumed> , 0x45299cd0) = 0
[pid  1555] write(22, "1555", 4)        = 4
[pid  1555] ioctl(21, 0xc0186201 <unfinished ...>
[pid  1554] <... ioctl resumed> , 0x45199cd0) = 0
[pid  1554] write(22, "1554", 4)        = 4

BUG=2660235

Change-Id: Ia9f9e1d5b792eaebc9560f89931faf6df0cf9c0d
parent 253e27ac

libcutils/sched_policy.c

+47 −32
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <string.h>

#include <errno.h>

#include <fcntl.h>

#include <pthread.h>



#define LOG_TAG "SchedPolicy"

#include "cutils/log.h"
@@ -42,15 +43,28 @@ 


#define POLICY_DEBUG 0



static pthread_once_t the_once = PTHREAD_ONCE_INIT;



static int __sys_supports_schedgroups = -1;



/* Add tid to the group defined by dev_path ("/dev/cpuctl/.../tasks") */

static int add_tid_to_cgroup(int tid, const char *dev_path)

// File descriptors open to /dev/cpuctl/../tasks, setup by initialize, or -1 on error.

static int normal_cgroup_fd = -1;

static int bg_cgroup_fd = -1;



/* Add tid to the scheduling group defined by the policy */

static int add_tid_to_cgroup(int tid, SchedPolicy policy)

{

    int fd;

    if ((fd = open(dev_path, O_WRONLY)) < 0) {

        SLOGE("add_tid_to_cgroup failed to open '%s' (%s)\n", dev_path,

             strerror(errno));



    if (policy == SP_BACKGROUND) {

        fd = bg_cgroup_fd;

    } else {

        fd = normal_cgroup_fd;

    }



    if (fd < 0) {

        SLOGE("add_tid_to_cgroup failed; background=%d\n",

              policy == SP_BACKGROUND ? 1 : 0);

        return -1;

    }
@@ -65,32 +79,40 @@ static int add_tid_to_cgroup(int tid, const char *dev_path) 
    }



    if (write(fd, ptr, end - ptr) < 0) {

        close(fd);

        /*

         * If the thread is in the process of exiting,

         * don't flag an error

         */

        if (errno == ESRCH)

                return 0;

        SLOGW("add_tid_to_cgroup failed to write '%s' to '%s' (%s)\n",

             ptr, dev_path, strerror(errno));

        SLOGW("add_tid_to_cgroup failed to write '%s' (%s); background=%d\n",

              ptr, strerror(errno), policy == SP_BACKGROUND ? 1 : 0);

        return -1;

    }



    close(fd);

    return 0;

}



static inline void initialize()

{

    if (__sys_supports_schedgroups < 0) {

static void __initialize(void) {

    char* filename;

    if (!access("/dev/cpuctl/tasks", F_OK)) {

        __sys_supports_schedgroups = 1;



        filename = "/dev/cpuctl/tasks";

        normal_cgroup_fd = open(filename, O_WRONLY);

        if (normal_cgroup_fd < 0) {

            SLOGE("open of %s failed: %s\n", filename, strerror(errno));

        }



        filename = "/dev/cpuctl/bg_non_interactive/tasks";

        bg_cgroup_fd = open(filename, O_WRONLY);

        if (bg_cgroup_fd < 0) {

            SLOGE("open of %s failed: %s\n", filename, strerror(errno));

        }

    } else {

        __sys_supports_schedgroups = 0;

    }

}

}



/*

 * Try to get the scheduler group.
@@ -166,7 +188,7 @@ static int getSchedulerGroup(int tid, char* buf, size_t bufLen) 


int get_sched_policy(int tid, SchedPolicy *policy)

{

    initialize();

    pthread_once(&the_once, __initialize);



    if (__sys_supports_schedgroups) {

        char grpBuf[32];
@@ -198,7 +220,7 @@ int get_sched_policy(int tid, SchedPolicy *policy) 


int set_sched_policy(int tid, SchedPolicy policy)

{

    initialize();

    pthread_once(&the_once, __initialize);



#if POLICY_DEBUG

    char statfile[64];
@@ -233,14 +255,7 @@ int set_sched_policy(int tid, SchedPolicy policy) 
#endif



    if (__sys_supports_schedgroups) {

        const char *dev_path;

        if (policy == SP_BACKGROUND) {

            dev_path = "/dev/cpuctl/bg_non_interactive/tasks";

        } else {

            dev_path = "/dev/cpuctl/tasks";

        }



        if (add_tid_to_cgroup(tid, dev_path)) {

        if (add_tid_to_cgroup(tid, policy)) {

            if (errno != ESRCH && errno != ENOENT)

                return -errno;

        }