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

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Message-ID: <4db4323f-3416-54a8-27e3-c491827a2fbd@rasmusvillemoes.dk>
Date:   Tue, 2 Apr 2019 21:02:16 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     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 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?

Rasmus