Messages in this thread | | | Date | Thu, 30 Jun 2016 18:38:47 +0800 | From | xinhui <> | Subject | Re: [RFC 12/12] x86/dumpstack: Optimize save_stack_trace |
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On 2016年06月29日 20:43, Byungchul Park wrote: > On Mon, Jun 20, 2016 at 04:50:37PM +0900, byungchul.park wrote: >>> -----Original Message----- >>> From: xinhui [mailto:xinhui.pan@linux.vnet.ibm.com] >>> Sent: Monday, June 20, 2016 4:29 PM >>> To: Byungchul Park; peterz@infradead.org; mingo@kernel.org >>> Cc: linux-kernel@vger.kernel.org; npiggin@suse.de; walken@google.com; >>> ak@suse.de; tglx@inhelltoy.tec.linutronix.de >>> Subject: Re: [RFC 12/12] x86/dumpstack: Optimize save_stack_trace >>> >>> >>> On 2016年06月20日 12:55, Byungchul Park wrote: >>>> Currently, x86 implementation of save_stack_trace() is walking all stack >>>> region word by word regardless of what the trace->max_entries is. >>>> However, it's unnecessary to walk after already fulfilling caller's >>>> requirement, say, if trace->nr_entries >= trace->max_entries is true. >>>> >>>> For example, CONFIG_LOCKDEP_CROSSRELEASE implementation calls >>>> save_stack_trace() with max_entries = 5 frequently. I measured its >>>> overhead and printed its difference of sched_clock() with my QEMU x86 >>>> machine. >>>> >>>> The latency was improved over 70% when trace->max_entries = 5. >>>> >>> [snip] >>> >>>> +static int save_stack_end(void *data) >>>> +{ >>>> + struct stack_trace *trace = data; >>>> + return trace->nr_entries >= trace->max_entries; >>>> +} >>>> + >>>> static const struct stacktrace_ops save_stack_ops = { >>>> .stack = save_stack_stack, >>>> .address = save_stack_address, >>> then why not check the return value of ->address(), -1 indicate there is >>> no room to store any pointer. >> >> Hello, >> >> Indeed. It also looks good to me even though it has to propagate the condition >> between callback functions. I will modify it if it's better. > > Do you also think it would be better to make it propagate the result of > ->address() rather than add a new callback, say, end_walk? > It's up to you. In my opinion, end_walk is better for reading.
>> >> Thank you. >> Byungchul >> >>> >>>> .walk_stack = print_context_stack, >>>> + .end_walk = save_stack_end, >>>> }; >>>> >>>> static const struct stacktrace_ops save_stack_ops_nosched = { >>>> >
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