From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>,
mingo@redhat.com, linux-kernel@vger.kernel.org,
He Kuang <hekuang@huawei.com>,
Alexei Starovoitov <ast@kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Brendan Gregg <brendan.d.gregg@gmail.com>,
Jiri Olsa <jolsa@kernel.org>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
Namhyung Kim <namhyung@kernel.org>, Zefan Li <lizefan@huawei.com>,
pi3orama@163.com
Subject: Re: [PATCH 2/5] perf core: Set event's default overflow_handler
Date: Wed, 23 Mar 2016 18:13:49 +0000 [thread overview]
Message-ID: <20160323181348.GA2149@arm.com> (raw)
In-Reply-To: <20160323175021.GK6356@twins.programming.kicks-ass.net>
On Wed, Mar 23, 2016 at 06:50:21PM +0100, Peter Zijlstra wrote:
> On Mon, Mar 14, 2016 at 09:59:42AM +0000, Wang Nan wrote:
> > +++ b/arch/arm/kernel/hw_breakpoint.c
> > @@ -631,7 +631,7 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
> > info->address &= ~alignment_mask;
> > info->ctrl.len <<= offset;
> >
> > - if (!bp->overflow_handler) {
> > + if (is_default_overflow_handler(bp)) {
> > /*
> > * Mismatch breakpoints are required for single-stepping
> > * breakpoints.
> > @@ -754,7 +754,7 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
> > * mismatch breakpoint so we can single-step over the
> > * watchpoint trigger.
> > */
> > - if (!wp->overflow_handler)
> > + if (is_default_overflow_handler(wp))
> > enable_single_step(wp, instruction_pointer(regs));
> >
> > unlock:
> > diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> > index b45c95d..4ef5373 100644
> > --- a/arch/arm64/kernel/hw_breakpoint.c
> > +++ b/arch/arm64/kernel/hw_breakpoint.c
> > @@ -616,7 +616,7 @@ static int breakpoint_handler(unsigned long unused, unsigned int esr,
> > perf_bp_event(bp, regs);
> >
> > /* Do we need to handle the stepping? */
> > - if (!bp->overflow_handler)
> > + if (is_default_overflow_handler(bp))
> > step = 1;
> > unlock:
> > rcu_read_unlock();
> > @@ -712,7 +712,7 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr,
> > perf_bp_event(wp, regs);
> >
> > /* Do we need to handle the stepping? */
> > - if (!wp->overflow_handler)
> > + if (is_default_overflow_handler(wp))
> > step = 1;
> >
> > unlock:
>
> Will, why does it matter what the overflow handler is for this stuff?
Because ptrace registers an overflow handler for raising a SIGTRAP and
ptrace users (e.g. GDB) expect to handle the single-stepping themselves.
Perf, on the other hand, will livelock if the kernel doesn't do the
stepping.
FWIW, I hate this whole thing. The only users of the perf side just seem
to be people running whacky test cases and then pointing out the places
where we're not identical to x86 :(
Will
next prev parent reply other threads:[~2016-03-23 18:13 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-14 9:59 [PATCH 0/5] perf core: Support overwrite ring buffer Wang Nan
2016-03-14 9:59 ` [PATCH 1/5] perf core: Introduce new ioctl options to pause and resume " Wang Nan
2016-03-23 9:16 ` Peter Zijlstra
2016-03-23 9:33 ` Wangnan (F)
2016-03-23 9:52 ` Peter Zijlstra
2016-03-23 12:43 ` Vince Weaver
2016-10-21 7:06 ` Michael Kerrisk (man-pages)
2016-10-21 7:13 ` Wangnan (F)
2016-10-21 8:55 ` Michael Kerrisk (man-pages)
2016-03-14 9:59 ` [PATCH 2/5] perf core: Set event's default overflow_handler Wang Nan
2016-03-23 17:50 ` Peter Zijlstra
2016-03-23 18:13 ` Will Deacon [this message]
2016-03-23 19:13 ` Peter Zijlstra
2016-03-23 19:29 ` Peter Zijlstra
2016-03-24 9:58 ` Will Deacon
2016-03-24 10:42 ` Peter Zijlstra
2016-03-14 9:59 ` [PATCH 3/5] perf core: Prepare writing into ring buffer from end Wang Nan
2016-03-23 9:50 ` Peter Zijlstra
2016-03-23 10:08 ` Wangnan (F)
2016-03-23 19:25 ` Alexei Starovoitov
2016-03-24 3:48 ` Wangnan (F)
2016-03-24 17:29 ` Alexei Starovoitov
2016-03-25 12:26 ` Wangnan (F)
2016-03-25 12:36 ` Wangnan (F)
2016-03-25 14:14 ` Wangnan (F)
2016-03-27 15:20 ` Peter Zijlstra
2016-03-27 15:30 ` pi3orama
2016-03-28 1:07 ` Wangnan (F)
2016-03-28 1:58 ` Wangnan (F)
2016-03-28 2:58 ` Wangnan (F)
2016-03-14 9:59 ` [PATCH 4/5] perf core: Add backward attribute to perf event Wang Nan
2016-03-14 9:59 ` [PATCH 5/5] perf core: Reduce perf event output overhead by new overflow handler Wang Nan
2016-03-23 10:02 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2016-01-25 8:33 [PATCH 0/5] perf core: Read from overwrite ring buffer Wang Nan
2016-01-25 8:33 ` [PATCH 2/5] perf core: Set event's default overflow_handler Wang Nan
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