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Commit 253e27ac authored by Brad Fitzpatrick's avatar Brad Fitzpatrick
Browse files

Optimize set_sched_policy(), which gets called in every binder call. 

- use static /dev/cpuctl filenames, rather than sprintf() on the fly
- use a custom formatter instead of sprintf() for the tid number

This is a simplified version of Dan's original
Ifc9c81f74fe65f0695ead53b30194bc6adf00da0 to be less risky for Froyo.

Bug: 2660235
Change-Id: I744bbc2ec01fd2569612c814a497df40a933b622
parent 458f0633

libcutils/sched_policy.c

+22 −16
Original line number Diff line number Diff line
@@ -44,22 +44,27 @@ 


static int __sys_supports_schedgroups = -1;



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

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

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

{

    int fd;

    char path[255];

    char text[64];



    sprintf(path, "/dev/cpuctl/%s/tasks", grp_name);



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

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

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

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

             strerror(errno));

        return -1;

    }



    sprintf(text, "%d", tid);

    if (write(fd, text, strlen(text)) < 0) {

    // specialized itoa -- works for tid > 0

    char text[22];

    char *end = text + sizeof(text) - 1;

    char *ptr = end;

    *ptr = '\0';

    while (tid > 0) {

        *--ptr = '0' + (tid % 10);

        tid = tid / 10;

    }



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

        close(fd);

	/*

	 * If the thread is in the process of exiting,
@@ -67,8 +72,8 @@ static int add_tid_to_cgroup(int tid, const char *grp_name) 
	 */

	if (errno == ESRCH)

		return 0;

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

             strerror(errno));

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

             ptr, dev_path, strerror(errno));

        return -1;

    }
@@ -228,13 +233,14 @@ int set_sched_policy(int tid, SchedPolicy policy) 
#endif



    if (__sys_supports_schedgroups) {

        const char *grp = "";



        const char *dev_path;

        if (policy == SP_BACKGROUND) {

            grp = "bg_non_interactive";

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

        } else {

            dev_path = "/dev/cpuctl/tasks";

        }



        if (add_tid_to_cgroup(tid, grp)) {

        if (add_tid_to_cgroup(tid, dev_path)) {

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

                return -errno;

        }