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Message-ID: <20150109164801.GW12302@n2100.arm.linux.org.uk>
Date: Fri, 9 Jan 2015 16:48:01 +0000
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Daniel Thompson <daniel.thompson@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Jason Cooper <jason@...edaemon.net>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
patches@...aro.org, linaro-kernel@...ts.linaro.org,
John Stultz <john.stultz@...aro.org>,
Sumit Semwal <sumit.semwal@...aro.org>,
Dirk Behme <dirk.behme@...bosch.com>,
Daniel Drake <drake@...lessm.com>,
Dmitry Pervushin <dpervushin@...il.com>,
Tim Sander <tim@...eglstein.org>,
Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH 3.19-rc2 v13 4/5] ARM: Add support for on-demand
backtrace of other CPUs
On Mon, Jan 05, 2015 at 10:19:25AM -0500, Steven Rostedt wrote:
> On Mon, 5 Jan 2015 14:54:58 +0000
> Daniel Thompson <daniel.thompson@...aro.org> wrote:
> > +/* For reliability, we're prepared to waste bits here. */
> > +static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
> > +static cpumask_t printtrace_mask;
> > +
> > +#define NMI_BUF_SIZE 4096
> > +
> > +struct nmi_seq_buf {
> > + unsigned char buffer[NMI_BUF_SIZE];
> > + struct seq_buf seq;
> > +};
Am I missing something or does this limit us to 4096 characters of
backtrace output per CPU?
> This is the same code as in x86. I wonder if we should move the
> duplicate code into kernel/printk/ and have it compiled if the arch
> requests it (CONFIG_ARCH_WANT_NMI_PRINTK or something). That way we
> don't have 20 copies of the same nmi_vprintk() and later find that we
> need to change it, and have to change it in 20 different archs.
Agreed, though I wonder about the buffer size.
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