From: catalin.marinas@arm•com (Catalin Marinas)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM: fix unwinding for XIP kernels
Date: Mon, 28 Nov 2011 10:07:31 +0000 [thread overview]
Message-ID: <20111128100731.GB1121@arm.com> (raw)
In-Reply-To: <20111128100219.GH17668@pengutronix.de>
On Mon, Nov 28, 2011 at 10:02:19AM +0000, Uwe Kleine-K?nig wrote:
> On Mon, Nov 28, 2011 at 09:45:03AM +0000, Catalin Marinas wrote:
> > On Mon, Nov 28, 2011 at 09:22:17AM +0000, Uwe Kleine-K?nig wrote:
> > > Hello,
> > >
> > > On Mon, Nov 21, 2011 at 06:35:45PM +0000, Catalin Marinas wrote:
> > > > On Sun, Nov 20, 2011 at 11:28:09AM +0000, Uwe Kleine-K?nig wrote:
> > > > > On Thu, Nov 17, 2011 at 02:17:06PM +0000, Catalin Marinas wrote:
> > > > > > On Thu, Nov 17, 2011 at 01:40:00PM +0000, Uwe Kleine-K?nig wrote:
> > > > > > > The linker places the unwind tables in readonly sections. So when using
> > > > > > > an XIP kernel these are located in ROM and cannot be modified.
> > > > > > >
> > > > > > > For that reason don't convert the symbol addresses during boot (or
> > > > > > > module loading) but only when interpreting them in search_index().
> > > > > > > Moreover several consts are added to catch future writes and rename the
> > > > > > > member "addr" of struct unwind_idx to "addr_offset" to better match the
> > > > > > > new semantic.
> > > > > > >
> > > > > > > This fixes unwinding on XIP which compared prel31 offsets to absolute
> > > > > > > addresses because the initial conversion from prel31 to absolute failed.
> > > > > >
> > > > > > My only worry - does this increase the index search by doing the prel31
> > > > > > conversion every time? It could affect tools like lockdep that need to
> > > > > > get the backtrace regularly at run-time.
> > > > > I did a first test now using
> > > > >
> > > > > static int __init unwind_test(void)
> > > >
> > > > With your latest patch, have you tried dropping __init from this
> > > > function? Since the .init.text section goes after the unwind_idx tables,
> > > > all the prel31 offsets are positive and the number of init functions is
> > > > smaller than the run-time ones.
> > > Yeah, it works fine. In fact unwinding unwind_test yields:
> > >
> > > do_one_initcall+0x50/0x158
> > > kernel_init+0x78/0x120
> > > kernel_thread_exit+0x0/0x8
> > >
> > > where kernel_thread_exit is not in .init.text, too.
> > >
> > > I don't know why you asked? Did you see a bug? Or is it just to let me
> > > do enough testing before you start reviewing my patches?
> >
> > It's not a bug, just a wondering about the performance figures you got
> > with your latest patch. When you have __init to unwind_test, the
> > .init.text functions are placed by the linker after the unwinding table,
> > with having a positive prel31 address. All the non-init functions are
> > placed before the table with a negative prel31. With your latest patch,
> > you split the set of functions in two ranges - the non-init one with a
> > negative prel31 and the init functions with a positive prel31 and the
> > binary search only happens on one of these ranges. The problem is that
> > the init range is much smaller than the non-init one, so your benchmark
> > figures may not be realistic.
> >
> > Could you run the simple benchmark on a non-init function?
> Without __init I get with the original implementation:
>
> 34139, 34127, 34100
>
> and with my patch I get
>
> 33456, 33425, 33407
>
> So the speedup here is smaller here, but still OK.
OK, so as long as it is not much worse than before, I'm ok with this.
I'll do a proper review of the patch in the next day or so.
Thanks.
--
Catalin
prev parent reply other threads:[~2011-11-28 10:07 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-17 13:40 [PATCH] ARM: fix unwinding for XIP kernels Uwe Kleine-König
2011-11-17 14:17 ` Catalin Marinas
2011-11-17 18:59 ` Uwe Kleine-König
2011-11-18 18:28 ` Nicolas Pitre
2011-11-18 21:36 ` Catalin Marinas
2011-11-20 11:28 ` Uwe Kleine-König
2011-11-20 22:52 ` Uwe Kleine-König
2011-11-20 23:12 ` [PATCH RFC] ARM: unwind: optimize to not convert each table value but the address Uwe Kleine-König
2011-11-21 16:34 ` Catalin Marinas
2011-11-21 18:16 ` Uwe Kleine-König
2011-11-30 17:58 ` Catalin Marinas
2011-11-30 19:07 ` [PATCH] ARM: fix unwinding for XIP kernels Uwe Kleine-König
2011-11-30 19:37 ` Nicolas Pitre
2011-11-30 19:52 ` Catalin Marinas
2011-11-21 18:35 ` Catalin Marinas
2011-11-28 9:22 ` Uwe Kleine-König
2011-11-28 9:45 ` Catalin Marinas
2011-11-28 10:02 ` Uwe Kleine-König
2011-11-28 10:07 ` Catalin Marinas [this message]
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