On Mon, Jul 04, 2016 at 07:27:54PM +0900, Byungchul Park wrote: > I suggested this patch on https://lkml.org/lkml/2016/6/20/22. However, > I want to proceed saperately since it's somewhat independent from each > other. Frankly speaking, I want this patchset to be accepted at first so > that the crossfeature can use this optimized save_stack_trace_norm() > which makes crossrelease work smoothly. > > ----->8----- > From 1ceb4cee520cfc562d5d63471f6db4e9a8d9ff42 Mon Sep 17 00:00:00 2001 > From: Byungchul Park <byungchul.p...@lge.com> > Date: Mon, 4 Jul 2016 18:31:09 +0900 > Subject: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace > > 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. > > 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. > > Before this patch: > > [ 2.326940] save_stack_trace() takes 83931 ns > [ 2.326389] save_stack_trace() takes 62576 ns > [ 2.327575] save_stack_trace() takes 58826 ns > [ 2.327000] save_stack_trace() takes 88980 ns > [ 2.327424] save_stack_trace() takes 59831 ns > [ 2.327575] save_stack_trace() takes 58482 ns > [ 2.327597] save_stack_trace() takes 87114 ns > [ 2.327931] save_stack_trace() takes 121140 ns > [ 2.327434] save_stack_trace() takes 64321 ns > [ 2.328632] save_stack_trace() takes 84997 ns > [ 2.328000] save_stack_trace() takes 115037 ns > [ 2.328460] save_stack_trace() takes 72292 ns > [ 2.328632] save_stack_trace() takes 61236 ns > [ 2.328567] save_stack_trace() takes 76666 ns > [ 2.328867] save_stack_trace() takes 79525 ns > [ 2.328460] save_stack_trace() takes 64902 ns > [ 2.329585] save_stack_trace() takes 58760 ns > [ 2.329000] save_stack_trace() takes 91349 ns > [ 2.329414] save_stack_trace() takes 60069 ns > [ 2.329585] save_stack_trace() takes 61012 ns > [ 2.329573] save_stack_trace() takes 76820 ns > [ 2.329863] save_stack_trace() takes 62131 ns > [ 2.330000] save_stack_trace() takes 99476 ns > [ 2.329846] save_stack_trace() takes 62419 ns > [ 2.330000] save_stack_trace() takes 88918 ns > [ 2.330253] save_stack_trace() takes 73669 ns > [ 2.330520] save_stack_trace() takes 67876 ns > [ 2.330671] save_stack_trace() takes 75963 ns > [ 2.330983] save_stack_trace() takes 95079 ns > [ 2.330451] save_stack_trace() takes 62352 ns > > After this patch: > > [ 2.780735] save_stack_trace() takes 19902 ns > [ 2.780718] save_stack_trace() takes 20240 ns > [ 2.781692] save_stack_trace() takes 45215 ns > [ 2.781477] save_stack_trace() takes 20191 ns > [ 2.781694] save_stack_trace() takes 20044 ns > [ 2.782589] save_stack_trace() takes 20292 ns > [ 2.782706] save_stack_trace() takes 20024 ns > [ 2.782706] save_stack_trace() takes 19881 ns > [ 2.782881] save_stack_trace() takes 24577 ns > [ 2.782706] save_stack_trace() takes 19901 ns > [ 2.783621] save_stack_trace() takes 24381 ns > [ 2.783621] save_stack_trace() takes 20205 ns > [ 2.783760] save_stack_trace() takes 19956 ns > [ 2.783718] save_stack_trace() takes 20280 ns > [ 2.784179] save_stack_trace() takes 20099 ns > [ 2.784835] save_stack_trace() takes 20055 ns > [ 2.785922] save_stack_trace() takes 20157 ns > [ 2.785922] save_stack_trace() takes 20140 ns > [ 2.786178] save_stack_trace() takes 20040 ns > [ 2.786877] save_stack_trace() takes 20102 ns > [ 2.795000] save_stack_trace() takes 21147 ns > [ 2.795397] save_stack_trace() takes 20230 ns > [ 2.795397] save_stack_trace() takes 31274 ns > [ 2.795739] save_stack_trace() takes 19706 ns > [ 2.796484] save_stack_trace() takes 20266 ns > [ 2.796484] save_stack_trace() takes 20902 ns > [ 2.797000] save_stack_trace() takes 38110 ns > [ 2.797510] save_stack_trace() takes 20224 ns > [ 2.798181] save_stack_trace() takes 20172 ns > [ 2.798837] save_stack_trace() takes 20824 ns > > Signed-off-by: Byungchul Park <byungchul.p...@lge.com> > --- > arch/x86/include/asm/stacktrace.h | 1 + > arch/x86/kernel/dumpstack.c | 4 ++++ > arch/x86/kernel/dumpstack_32.c | 2 ++ > arch/x86/kernel/stacktrace.c | 7 +++++++ > 4 files changed, 14 insertions(+) > > diff --git a/arch/x86/include/asm/stacktrace.h > b/arch/x86/include/asm/stacktrace.h > index 70bbe39..fc572e7 100644 > --- a/arch/x86/include/asm/stacktrace.h > +++ b/arch/x86/include/asm/stacktrace.h > @@ -41,6 +41,7 @@ struct stacktrace_ops { > /* On negative return stop dumping */ > int (*stack)(void *data, char *name); > walk_stack_t walk_stack; > + int (*end_walk)(void *data); > }; > > void dump_trace(struct task_struct *tsk, struct pt_regs *regs, > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c > index 9c30acf..89f68f3 100644 > --- a/arch/x86/kernel/dumpstack.c > +++ b/arch/x86/kernel/dumpstack.c > @@ -115,6 +115,8 @@ print_context_stack(struct thread_info *tinfo, > print_ftrace_graph_addr(addr, data, ops, tinfo, graph); > } > stack++; > + if (ops->end_walk && ops->end_walk(data)) > + break;
Instead of adding a new callback, why not just check the ops->address() return value? It already returns an error if the array is full. I think that would be cleaner and would help prevent more callback sprawl. > } > return bp; > } > @@ -139,6 +141,8 @@ print_context_stack_bp(struct thread_info *tinfo, > frame = frame->next_frame; > ret_addr = &frame->return_address; > print_ftrace_graph_addr(addr, data, ops, tinfo, graph); > + if (ops->end_walk && ops->end_walk(data)) > + break; Same here, and print_context_stack_bp() already checks the ops->address() return value anyway. -- Josh