Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161128AbVLWXP6 (ORCPT ); Fri, 23 Dec 2005 18:15:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161129AbVLWXP6 (ORCPT ); Fri, 23 Dec 2005 18:15:58 -0500 Received: from ns1.siteground.net ([207.218.208.2]:17592 "EHLO serv01.siteground.net") by vger.kernel.org with ESMTP id S1161128AbVLWXP5 (ORCPT ); Fri, 23 Dec 2005 18:15:57 -0500 Date: Fri, 23 Dec 2005 15:15:49 -0800 From: Ravikiran G Thirumalai To: Christoph Lameter , Andrew Morton Cc: linux-kernel@vger.kernel.org, "Shai Fultheim (Shai@scalex86.org)" , nippung@calsoftinc.com Subject: Re: [rfc][patch] Avoid taking global tasklist_lock for single threaded process at getrusage() Message-ID: <20051223231549.GA3848@localhost.localdomain> References: <20051221182320.GA4514@localhost.localdomain> <20051221211135.GB4514@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - serv01.siteground.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [0 0] / [47 12] X-AntiAbuse: Sender Address Domain - scalex86.org X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 14006 Lines: 409 On Wed, Dec 21, 2005 at 01:22:24PM -0800, Christoph Lameter wrote: > On Wed, 21 Dec 2005, Ravikiran G Thirumalai wrote: > > > We did look at that. Cases RUSAGE_CHILDREN and RUSAGE_SELF are always called by the > > current task, so we can avoid tasklist locking there. > > getrusage for non-current tasks are always called with RUSAGE_BOTH. > > We ensure we always take the siglock for RUSAGE_BOTH case, so that the > > p->signal* fields are protected and take the tasklist_lock only if we have > > to traverse the tasklist hashlist. Isn't this safe? > > Sounds okay. But its complex in the way its is coded now and its easy to > assume that one can call getrusage with any parameter from inside the > kernel. Maybe we can have a couple of separate functions > > rusage_children() > rusage_self() > rusage_both() > > ? > > Only rusage_both would take a task_struct * parameter. The others would > only operate on current. Change all the locations that call getrusage with > RUSAGE_BOTH to call rusage_both(). Here is the modified patch. Andrew, pleas apply. --- Following patch avoids taking the global tasklist_lock when possible, if a process is single threaded during getrusage(). Any avoidance of tasklist_lock is good for NUMA boxes (and possibly for large SMPs). We found that this optimization reduces the runtime of a certain scientific application by half on a 16 cpu NUMA box. This optimization is similar to the sys_times tasklist_lock optimization. Change from prev post: Split getrusage to getrusage_self, getrusage_children and getrusage_both. Signed-off-by: Nippun Goel Signed-off-by: Ravikiran Thirumalai Signed-off-by: Shai Fultheim Index: linux-2.6.15-rc6/arch/mips/kernel/irixsig.c =================================================================== --- linux-2.6.15-rc6.orig/arch/mips/kernel/irixsig.c 2005-12-19 15:17:51.000000000 -0800 +++ linux-2.6.15-rc6/arch/mips/kernel/irixsig.c 2005-12-23 10:42:16.000000000 -0800 @@ -540,7 +540,7 @@ #define IRIX_P_PGID 2 #define IRIX_P_ALL 7 -extern int getrusage(struct task_struct *, int, struct rusage __user *); +extern int getrusage_both(struct task_struct *, struct rusage __user *); #define W_EXITED 1 #define W_TRAPPED 2 @@ -605,7 +605,7 @@ remove_parent(p); add_parent(p, p->parent); write_unlock_irq(&tasklist_lock); - retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0; + retval = ru ? getrusage_both(p, ru) : 0; if (retval) goto end_waitsys; @@ -626,7 +626,7 @@ current->signal->cutime += p->utime + p->signal->cutime; current->signal->cstime += p->stime + p->signal->cstime; if (ru != NULL) - getrusage(p, RUSAGE_BOTH, ru); + getrusage_both(p, ru); retval = __put_user(SIGCHLD, &info->sig); retval |= __put_user(1, &info->code); /* CLD_EXITED */ retval |= __put_user(p->pid, &info->stuff.procinfo.pid); Index: linux-2.6.15-rc6/arch/mips/kernel/sysirix.c =================================================================== --- linux-2.6.15-rc6.orig/arch/mips/kernel/sysirix.c 2005-12-19 15:17:51.000000000 -0800 +++ linux-2.6.15-rc6/arch/mips/kernel/sysirix.c 2005-12-23 10:42:16.000000000 -0800 @@ -234,7 +234,8 @@ #undef DEBUG_PROCGRPS extern unsigned long irix_mapelf(int fd, struct elf_phdr __user *user_phdrp, int cnt); -extern int getrusage(struct task_struct *p, int who, struct rusage __user *ru); +extern int getrusage_self(struct rusage __user *ru); +extern int getrusage_children(struct rusage __user *ru); extern char *prom_getenv(char *name); extern long prom_setenv(char *name, char *value); @@ -405,12 +406,12 @@ switch((int) regs->regs[base + 5]) { case 0: /* rusage self */ - retval = getrusage(current, RUSAGE_SELF, ru); + retval = getrusage_self(ru); goto out; case -1: /* rusage children */ - retval = getrusage(current, RUSAGE_CHILDREN, ru); + retval = getrusage_children(ru); goto out; default: Index: linux-2.6.15-rc6/kernel/exit.c =================================================================== --- linux-2.6.15-rc6.orig/kernel/exit.c 2005-12-19 15:17:55.000000000 -0800 +++ linux-2.6.15-rc6/kernel/exit.c 2005-12-23 10:42:16.000000000 -0800 @@ -38,7 +38,7 @@ extern void sem_exit (void); extern struct task_struct *child_reaper; -int getrusage(struct task_struct *, int, struct rusage __user *); +int getrusage_both(struct task_struct *, struct rusage __user *); static void exit_mm(struct task_struct * tsk); @@ -994,7 +994,7 @@ struct siginfo __user *infop, struct rusage __user *rusagep) { - int retval = rusagep ? getrusage(p, RUSAGE_BOTH, rusagep) : 0; + int retval = rusagep ? getrusage_both(p, rusagep) : 0; put_task_struct(p); if (!retval) retval = put_user(SIGCHLD, &infop->si_signo); @@ -1111,7 +1111,7 @@ */ read_unlock(&tasklist_lock); - retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0; + retval = ru ? getrusage_both(p, ru) : 0; status = (p->signal->flags & SIGNAL_GROUP_EXIT) ? p->signal->group_exit_code : p->exit_code; if (!retval && stat_addr) @@ -1260,7 +1260,7 @@ write_unlock_irq(&tasklist_lock); - retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0; + retval = ru ? getrusage_both(p, ru) : 0; if (!retval && stat_addr) retval = put_user((exit_code << 8) | 0x7f, stat_addr); if (!retval && infop) @@ -1321,7 +1321,7 @@ read_unlock(&tasklist_lock); if (!infop) { - retval = ru ? getrusage(p, RUSAGE_BOTH, ru) : 0; + retval = ru ? getrusage_both(p, ru) : 0; put_task_struct(p); if (!retval && stat_addr) retval = put_user(0xffff, stat_addr); Index: linux-2.6.15-rc6/kernel/sys.c =================================================================== --- linux-2.6.15-rc6.orig/kernel/sys.c 2005-12-23 10:41:47.000000000 -0800 +++ linux-2.6.15-rc6/kernel/sys.c 2005-12-23 12:08:32.000000000 -0800 @@ -1657,6 +1657,10 @@ } /* + * getrusage routines: + * getrusage_self() and getrusage_children() always use current. + * getrusage_both() need not be for the current task. + * * It would make sense to put struct rusage in the task_struct, * except that would make the task_struct be *really big*. After * task_struct gets moved into malloc'ed memory, it would @@ -1664,9 +1668,6 @@ * a lot simpler! (Which we're not doing right now because we're not * measuring them yet). * - * This expects to be called with tasklist_lock read-locked or better, - * and the siglock not locked. It may momentarily take the siglock. - * * When sampling multiple threads for RUSAGE_SELF, under SMP we might have * races with threads incrementing their own counters. But since word * reads are atomic, we either get new values or old values and we don't @@ -1674,84 +1675,166 @@ * the c* fields from p->signal from races with exit.c updating those * fields when reaping, so a sample either gets all the additions of a * given child after it's reaped, or none so this sample is before reaping. + * + * Locking semantics for the following three functions: + * + * If we have a multithreaded process, we need to take tasklist read lock + * for getrusage_self() and getrusage_both(). We don't need to take the + * tasklist lock for getrusage_children() and just the siglock should + * suffice there. + * + * If we are a single threaded process, we donot need to take the tasklist_lock + * for reading the non c* vars from struct signal. However, we need to take + * siglock for the getrusage_both() case to access the c* fields from signal. + * getrusage_self() and getrusage_children() are for the current process, + * unlike getrusage_both(). So not taking siglock for SELF and CHILDREN + * cases is safe. + * + * In the multithreaded scenario, while we have the tasklist_lock held for + * read, the non c* p->signal field updates cannot take place as the + * __exit_signal thread is called with write lock taken on tasklist_lock. + * Reads on the p->signal c* fields however can race if a child is being reaped. + * we avoid the race by taking the siglock to read the c* fileds. + * + * Hence, tasklist lock for read is sufficient for getrusage_self() */ -static void k_getrusage(struct task_struct *p, int who, struct rusage *r) +int getrusage_children(struct rusage __user *ru) { - struct task_struct *t; unsigned long flags; + int lockflag = 0; cputime_t utime, stime; - - memset((char *) r, 0, sizeof *r); + struct rusage r; + struct task_struct *p = current; + memset((char *) &r, 0, sizeof (r)); if (unlikely(!p->signal)) - return; + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0; - switch (who) { - case RUSAGE_CHILDREN: - spin_lock_irqsave(&p->sighand->siglock, flags); - utime = p->signal->cutime; - stime = p->signal->cstime; - r->ru_nvcsw = p->signal->cnvcsw; - r->ru_nivcsw = p->signal->cnivcsw; - r->ru_minflt = p->signal->cmin_flt; - r->ru_majflt = p->signal->cmaj_flt; - spin_unlock_irqrestore(&p->sighand->siglock, flags); - cputime_to_timeval(utime, &r->ru_utime); - cputime_to_timeval(stime, &r->ru_stime); - break; - case RUSAGE_SELF: - spin_lock_irqsave(&p->sighand->siglock, flags); - utime = stime = cputime_zero; - goto sum_group; - case RUSAGE_BOTH: - spin_lock_irqsave(&p->sighand->siglock, flags); - utime = p->signal->cutime; - stime = p->signal->cstime; - r->ru_nvcsw = p->signal->cnvcsw; - r->ru_nivcsw = p->signal->cnivcsw; - r->ru_minflt = p->signal->cmin_flt; - r->ru_majflt = p->signal->cmaj_flt; - sum_group: - utime = cputime_add(utime, p->signal->utime); - stime = cputime_add(stime, p->signal->stime); - r->ru_nvcsw += p->signal->nvcsw; - r->ru_nivcsw += p->signal->nivcsw; - r->ru_minflt += p->signal->min_flt; - r->ru_majflt += p->signal->maj_flt; - t = p; - do { - utime = cputime_add(utime, t->utime); - stime = cputime_add(stime, t->stime); - r->ru_nvcsw += t->nvcsw; - r->ru_nivcsw += t->nivcsw; - r->ru_minflt += t->min_flt; - r->ru_majflt += t->maj_flt; - t = next_thread(t); - } while (t != p); - spin_unlock_irqrestore(&p->sighand->siglock, flags); - cputime_to_timeval(utime, &r->ru_utime); - cputime_to_timeval(stime, &r->ru_stime); - break; - default: - BUG(); + if (!thread_group_empty(p)) { + spin_lock_irqsave(&p->sighand->siglock, flags); + lockflag = 1; + } + + utime = p->signal->cutime; + stime = p->signal->cstime; + r.ru_nvcsw = p->signal->cnvcsw; + r.ru_nivcsw = p->signal->cnivcsw; + r.ru_minflt = p->signal->cmin_flt; + r.ru_majflt = p->signal->cmaj_flt; + if (lockflag) + spin_unlock_irqrestore(&p->sighand->siglock, flags); + cputime_to_timeval(utime, &r.ru_utime); + cputime_to_timeval(stime, &r.ru_stime); + + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0; +} + +int getrusage_self(struct rusage __user *ru) +{ + int lockflag = 0; + cputime_t utime, stime; + struct rusage r; + struct task_struct *t, *p = current; + + memset((char *) &r, 0, sizeof (r)); + + if (unlikely(!p->signal)) + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0; + if (!thread_group_empty(p)) { + read_lock(&tasklist_lock); + lockflag = 1; } + + utime = p->signal->utime; + stime = p->signal->stime; + r.ru_nvcsw = p->signal->nvcsw; + r.ru_nivcsw = p->signal->nivcsw; + r.ru_minflt = p->signal->min_flt; + r.ru_majflt = p->signal->maj_flt; + t = p; + do { + utime = cputime_add(utime, t->utime); + stime = cputime_add(stime, t->stime); + r.ru_nvcsw += t->nvcsw; + r.ru_nivcsw += t->nivcsw; + r.ru_minflt += t->min_flt; + r.ru_majflt += t->maj_flt; + t = next_thread(t); + } while (t != p); + + if (lockflag) + read_unlock(&tasklist_lock); + cputime_to_timeval(utime, &r.ru_utime); + cputime_to_timeval(stime, &r.ru_stime); + + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0; } -int getrusage(struct task_struct *p, int who, struct rusage __user *ru) + +int getrusage_both(struct task_struct *p, struct rusage __user *ru) { + unsigned long flags; + int lockflag = 0; + cputime_t utime, stime; struct rusage r; - read_lock(&tasklist_lock); - k_getrusage(p, who, &r); - read_unlock(&tasklist_lock); + struct task_struct *t; + memset((char *) &r, 0, sizeof (r)); + + if (unlikely(!p->signal)) + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0; + + if (!thread_group_empty(p)) { + read_lock(&tasklist_lock); + lockflag = 1; + } + + spin_lock_irqsave(&p->sighand->siglock, flags); + utime = p->signal->cutime; + stime = p->signal->cstime; + r.ru_nvcsw = p->signal->cnvcsw; + r.ru_nivcsw = p->signal->cnivcsw; + r.ru_minflt = p->signal->cmin_flt; + r.ru_majflt = p->signal->cmaj_flt; + spin_unlock_irqrestore(&p->sighand->siglock, flags); + + utime = cputime_add(utime, p->signal->utime); + stime = cputime_add(stime, p->signal->stime); + r.ru_nvcsw += p->signal->nvcsw; + r.ru_nivcsw += p->signal->nivcsw; + r.ru_minflt += p->signal->min_flt; + r.ru_majflt += p->signal->maj_flt; + + t = p; + do { + utime = cputime_add(utime, t->utime); + stime = cputime_add(stime, t->stime); + r.ru_nvcsw += t->nvcsw; + r.ru_nivcsw += t->nivcsw; + r.ru_minflt += t->min_flt; + r.ru_majflt += t->maj_flt; + t = next_thread(t); + } while (t != p); + + if (lockflag) + read_unlock(&tasklist_lock); + cputime_to_timeval(utime, &r.ru_utime); + cputime_to_timeval(stime, &r.ru_stime); + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0; } asmlinkage long sys_getrusage(int who, struct rusage __user *ru) { - if (who != RUSAGE_SELF && who != RUSAGE_CHILDREN) - return -EINVAL; - return getrusage(current, who, ru); + switch (who) { + case RUSAGE_SELF: + return getrusage_self(ru); + case RUSAGE_CHILDREN: + return getrusage_children(ru); + default: + break; + } + return -EINVAL; } asmlinkage long sys_umask(int mask) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/