linux-kernel - Re: [patch 15/14] x86/dumpstack/64: Speedup in_exception

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Message-ID: <alpine.DEB.2.21.1904022109250.1812@nanos.tec.linutronix.de>
Date:   Tue, 2 Apr 2019 21:21:34 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [patch 15/14] x86/dumpstack/64: Speedup in_exception_stack()

On Tue, 2 Apr 2019, Rasmus Villemoes wrote:

> On 02/04/2019 17.48, Thomas Gleixner wrote:
> > On Tue, 2 Apr 2019, Josh Poimboeuf wrote:
> >> On Tue, Apr 02, 2019 at 12:19:46PM +0200, Thomas Gleixner wrote:
> >>> +/*
> >>> + * Array of exception stack page descriptors. If the stack is larger than
> >>> + * PAGE_SIZE, all pages covering a particular stack will have the same
> >>> + * info.
> >>> + */
> >>> +static const struct estack_pages estack_pages[ESTACK_PAGES] ____cacheline_aligned = {
> >>> +	[CONDRANGE(DF)]		= ESTACK_PAGE(DOUBLEFAULT_IST, DF),
> >>> +	[CONDRANGE(NMI)]	= ESTACK_PAGE(NMI_IST, NMI),
> >>> +	[PAGERANGE(DB)]		= ESTACK_PAGE(DEBUG_IST, DB),
> >>> +	[CONDRANGE(MCE)]	= ESTACK_PAGE(MCE_IST, MCE),
> >>
> >> It would be nice if the *_IST macro naming aligned with the struct
> >> cea_exception_stacks field naming.  Then you could just do, e.g.
> >> ESTACKPAGE(DF).
> > 
> > Yes, lemme fix that up.
> > 
> >> Also it's a bit unfortunate that some of the stack size knowledge is
> >> hard-coded here, i.e #DB always being > 1 page and non-#DB being
> >> sometimes 1 page.
> > 
> > The problem is that there is no way to make this macro maze conditional on
> > sizeof(). But my macro foo is rusty.
> 
> Eh, but why do you need the CONDRANGE thing at all? [5 ... 5] is a
> perfectly fine designator, equivalent to [5]. So you can just use
> PAGERANGE in all cases, no?

Indeed. I tried that before and at some point GCC barfed, but probably due
to some other slipup. The macro expansion error messages are soo helpful...

Thanks,

	tglx