Messages in this thread | | | Date | Wed, 21 Jul 2010 14:49:44 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Don't apply for write lock on tasklist_lock if parent doesn't ptrace other processes |
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On Thu, 15 Jul 2010 14:51:03 +0800 "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote:
> We run some sub-cases (fork, exec, pipe, tcp, udp) of aim7 on 8-socket machine. > Perf shows write_lock_irq(&tasklist_lock) consumes more than 50% cpu time. > > One hot caller is exit_ptrace. If the exiting process doesn't ptrace other > processes, kernel needn't apply for the write lock on tasklist_lock. > > With below patch against kernel 2.6.35-rc5, we get more than 10% result improvement. > > Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com> > > --- > > diff -Nraup linux-2.6.35-rc5/kernel/ptrace.c linux-2.6.35-rc5_ptrace/kernel/ptrace.c > --- linux-2.6.35-rc5/kernel/ptrace.c 2010-07-16 14:01:15.000000000 +0800 > +++ linux-2.6.35-rc5_ptrace/kernel/ptrace.c 2010-07-16 14:03:20.000000000 +0800 > @@ -331,6 +331,9 @@ void exit_ptrace(struct task_struct *tra > struct task_struct *p, *n; > LIST_HEAD(ptrace_dead); > > + if (list_empty(&tracer->ptraced)) > + return; > + > write_lock_irq(&tasklist_lock); > list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) { > if (__ptrace_detach(tracer, p))
hah, nice patch - an easy 10%. I snuck a cc:stable into the changelog in the hope that those guys mistake it for a bugfix ;)
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