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perf: Fix inconsistency between IP and callchain sampling 

When running perf across all cpus with backtracing (-a -g), sometimes we
get samples without associated backtraces:

    23.44%         init  [kernel]                     [k] restore
    11.46%         init                       eeba0c  [k] 0x00000000eeba0c
     6.77%      swapper  [kernel]                     [k] .perf_ctx_adjust_freq
     5.73%         init  [kernel]                     [k] .__trace_hcall_entry
     4.69%         perf  libc-2.9.so                  [.] 0x0000000006bb8c
                       |
                       |--11.11%-- 0xfffa941bbbc

It turns out the backtrace code has a check for the idle task and the IP
sampling does not. This creates problems when profiling an interrupt
heavy workload (in my case 10Gbit ethernet) since we get no backtraces
for interrupts received while idle (ie most of the workload).

Right now x86 and sh check that current is not NULL, which should never
happen so remove that too.

Idle task's exclusion must be performed from the core code, on top
of perf_event_attr:exclude_idle.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mundt <lethal@linux-sh.org>
LKML-Reference: <20100118054707.GT12666@kryten>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
This commit is contained in:
Anton Blanchard 2010-01-18 16:47:07 +11:00 committed by Frederic Weisbecker
parent 408f0d18ba
commit 339ce1a4dc
3 changed files with 0 additions and 9 deletions
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3
arch/powerpc/kernel/perf_callchain.c
View File

@ -495,9 +495,6 @@ struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
entry->nr = 0;
if (current->pid == 0) /* idle task? */
return entry;
if (!user_mode(regs)) {
perf_callchain_kernel(regs, entry);
if (current->mm)

3
arch/sh/kernel/perf_callchain.c
View File

@ -68,9 +68,6 @@ perf_do_callchain(struct pt_regs *regs, struct perf_callchain_entry *entry)
is_user = user_mode(regs);
if (!current || current->pid == 0)
return;
if (is_user && current->state != TASK_RUNNING)
return;

3
arch/x86/kernel/cpu/perf_event.c
View File

@ -2425,9 +2425,6 @@ perf_do_callchain(struct pt_regs *regs, struct perf_callchain_entry *entry)
is_user = user_mode(regs);
if (!current || current->pid == 0)
return;
if (is_user && current->state != TASK_RUNNING)
return;