linux-kernel - Re: [PATCH v5 12/20] x86: perf: intel

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Message-ID: <87zjcl290d.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Fri, 24 Oct 2014 10:59:30 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, acme@...radead.org
Subject: Re: [PATCH v5 12/20] x86: perf: intel_pt: Intel PT PMU driver

Peter Zijlstra <peterz@...radead.org> writes:

>> +/* make negative table index stand for the last table entry */
>> +#define TOPA_ENTRY(t, i) ((i) == -1 ? &(t)->table[(t)->last] : &(t)->table[(i)])
>
> code does not match comment; negative would be: i < 0, not i == -1.

Indeed.

> Something like: ({ if (i < 0) i += t->size; t->table[i]; }), might work,
> of course that goes bang when: i !e [-size,size)

Table indices and sizes are measured in different units. Using -1 to
mean the last is just a small convenience, in the code it would be used
explicitly as TOPA_ENTRY(topa, -1).end = 1, for example.

Regards,
--
Alex
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