Hi Steve, Could you please explain what this error means? Is it related to length of subject? I have run checkpatch.pl on patch and didn't show any error.
Thanks, Soumya. -----Original Message----- From: Steven Rostedt [mailto:rost...@goodmis.org] Sent: Thursday, May 19, 2016 1:25 AM To: N, Soumya P <soumya....@hpe.com> Cc: mi...@redhat.com; linux-kernel@vger.kernel.org Subject: Re: [PATCH] ftrace: As disabling interrupts is costly and write_lock variant of tasklist_lock is not held from interrupt context it is not necessary to disable interrupts. -ERUNONSUBJECT -- Steve On Tue, 17 May 2016 21:31:14 +0530 Soumya PN <soumya....@hpe.com> wrote: > In ftrace.c inside the function alloc_retstack_tasklist()(which will > be invoked when function_graph tracing is on) the tasklist_lock is > being held as reader while iterating through list of threads. Here the > lock is being held as reader with irqs disabled. The tasklist_lock is > never write_locked in interrupt context so it is safe to not disable > interrupts for the duration of read_lock in this block which, can be > significant, given the block of code iterates through all threads. > Hence changing the code to call read_lock() and read_unlock() instead > of read_lock_irqsave() and read_unlock_irqrestore(). Seen the same > change is made in "kernel/tracepoint.c" and "kernel/sched/core.c"files > with commit ids 'commit 8063e41d2ffc ("tracing: Change > syscall_*regfunc() to check PF_KTHREAD and use for_each_process_thread()")' > 'commit 3472eaa1f12e ("sched: normalize_rt_tasks(): Don't use _irqsave > for tasklist_lock, use task_rq_lock()")' > > Stopped the irqbalance service and bound the interrupts and processes > being traced to the same cpu core with function_graph tracing on. I/Os > completed successfully. Verified the trace output and seen the > expected results. > > Signed-off-by: Soumya PN <soumya....@hpe.com> > --- > kernel/trace/ftrace.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index > b1870fb..a680482 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -5713,7 +5713,6 @@ static int alloc_retstack_tasklist(struct > ftrace_ret_stack **ret_stack_list) { > int i; > int ret = 0; > - unsigned long flags; > int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE; > struct task_struct *g, *t; > > @@ -5729,7 +5728,7 @@ static int alloc_retstack_tasklist(struct > ftrace_ret_stack **ret_stack_list) > } > } > > - read_lock_irqsave(&tasklist_lock, flags); > + read_lock(&tasklist_lock); > do_each_thread(g, t) { > if (start == end) { > ret = -EAGAIN; > @@ -5747,7 +5746,7 @@ static int alloc_retstack_tasklist(struct > ftrace_ret_stack **ret_stack_list) > } while_each_thread(g, t); > > unlock: > - read_unlock_irqrestore(&tasklist_lock, flags); > + read_unlock(&tasklist_lock); > free: > for (i = start; i < end; i++) > kfree(ret_stack_list[i]);
