linux-kernel - Re: [PATCH 02/10] perf, tools: Support handling complete branch stacks as histograms

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Date:	Thu, 13 Nov 2014 17:42:22 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	jolsa@...hat.com, linux-kernel@...r.kernel.org,
	namhyung@...nel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 02/10] perf, tools: Support handling complete branch
 stacks as histograms

Em Thu, Nov 13, 2014 at 09:15:24PM +0100, Andi Kleen escreveu:
> On Thu, Nov 13, 2014 at 05:08:33PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Nov 13, 2014 at 08:52:08PM +0100, Andi Kleen escreveu:
> > > On Thu, Nov 13, 2014 at 04:14:17PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > Em Wed, Nov 12, 2014 at 06:05:20PM -0800, Andi Kleen escreveu:
> > > > > +static int remove_loops(struct branch_entry *l, int nr)
> > > > > +{
> > > > > +	int i, j, off;
> > > > > +	unsigned char chash[CHASHSZ];
> > > > > +
> > > > > +	memset(chash, NO_ENTRY, sizeof(chash));
> > > > > +
> > > > > +	BUG_ON(nr >= 256);
> > > > 
> > > > What is wrong with return -1 and propagating the error, so that the user
> > > > is informed if the data being processed is bogus, stop processing with a
> > > > warning or continue processing if finding the next valid record is
> > > > possible?
> > > 
> > > The error doesn't depend on the record. There is a check for the record
> > > being < 127 in front of this. This is merely to catch that 
> > > if someone increases PERF_MAX_BRANCH_DEPTH to below 255 they need
> > > to increase the type of the hash table from u8.
> > 
> > Ok, so this would be better as a BUILD_BUG_ON? 
> 
> Yes that should work.

Ok, I'll do that, test by bumping it to 256, etc and merge the resulting
patch, thanks for checking.

- Arnaldo
 
> -Andi
> 
> > 
> > Like:
> > 
> > #define CHASHSZ 127
> > #define CHASHBITS 7
> > #define NO_ENTRY 0xff
> > 
> > #define PERF_MAX_BRANCH_DEPTH 127
> > 
> > /* Remove loops. */
> > static int remove_loops(struct branch_entry *l, int nr)
> > {
> > 	int i, j, off;
> > 	unsigned char chash[CHASHSZ];
> > 
> > 	memset(chash, NO_ENTRY, sizeof(chash));
> > 
> > 	/* Change the type of the chash table, u8 is not enough now */
> > 	BUILD_BUG_ON(PERF_MAX_BRANCH_DEPTH >= 256);
> > 	for (i = 0; i < nr; i++) {
> > 		int h = hash_64(l[i].from, CHASHBITS) % CHASHSZ;
> > 
> > -------------------------------------
> > 
> > - Arnaldo
> > 
> 
> -- 
> ak@...ux.intel.com -- Speaking for myself only.
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