[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20190419094313.GO7905@worktop.programming.kicks-ass.net>
Date: Fri, 19 Apr 2019 11:43:13 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Kairui Song <kasong@...hat.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Namhyung Kim <namhyung@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC PATCH v3] perf/x86: make perf callchain work without
CONFIG_FRAME_POINTER
On Fri, Apr 19, 2019 at 10:17:49AM +0800, Kairui Song wrote:
> On Fri, Apr 19, 2019 at 8:58 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > I still don't like using regs->bp because it results in different code
> > paths for FP and ORC. In the FP case, the regs are treated like real
> > regs even though they're fake.
> >
> > Something like the below would be much simpler. Would this work? I don't
> > know if any other code relies on the fake regs->bp or regs->sp.
>
> Works perfectly. My only concern is that FP path used to work very
> well, not sure it's a good idea to change it, and this may bring some
> extra overhead for FP path.
Given Josh wrote all that code, I'm fairly sure it is still OK :-)
But also looking at the code in unwind_frame.c, __unwind_start() seems
to pretty much do what the removed caller_frame_pointer() did (when
.regs=NULL) but better.
> > + if (perf_hw_regs(regs)) {
> > + if (perf_callchain_store(entry, regs->ip))
> > + return;
> > + unwind_start(&state, current, regs, NULL);
> > + } else {
> > + unwind_start(&state, current, NULL, (void *)regs->sp);
> > + }
> > #define perf_arch_fetch_caller_regs(regs, __ip) { \
> > (regs)->ip = (__ip); \
> > + (regs)->sp = (unsigned long)__builtin_frame_address(0); \
> > (regs)->cs = __KERNEL_CS; \
> > regs->flags = 0; \
> > }
Powered by blists - more mailing lists