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From: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
To: gcc-patches@gcc.gnu.org, "Martin Liška" <mliska@suse.cz>
Cc: Jason Merrill <jason@redhat.com>,Jan Hubicka <hubicka@ucw.cz>
Subject: Re: [PATCH] Improve predictions for hot and cold labels ([[likely]], [[unlikely]]).
Date: Thu, 06 Dec 2018 08:26:00 -0000	[thread overview]
Message-ID: <0BBB0656-0D20-4299-B15D-CBC39A84DC23@gmail.com> (raw)
In-Reply-To: <cbe66900-a132-7157-99f1-765c43368295@suse.cz>

On 30 November 2018 10:47:45 CET, "Martin Liška" <mliska@suse.cz> wrote:
>Hi.
>
>This patch is a reaction to Jason's commit where he introduced new C++
>attributes.
>First I would like to align cold/hot to __builtin_expect, so I adjusted
>probability
>and made the predictors first match predictors.
>
>Second I fixed how we consider the predictors in switch statements, so
>that
>we can correctly predict situation in predict-3.
>
>Honza is fine with the patch, I'll install it later if there are no
>objections.
>Survives tests and bootstrap on xc86_64-linux-gnu.

I don't have the sources at hand but in:

+/* Branches to hot labels are likely.  */
+DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (90),
+	       PRED_FLAG_FIRST_MATCH)
+
+/* Branches to cold labels are extremely unlikely.  */
+DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", HITRATE (90),
+	       PRED_FLAG_FIRST_MATCH)
+

I would have expected cold labels to have a rather low hitrate, like maybe 2 or 7, not 90 ?

Thanks,

  reply	other threads:[~2018-12-06  8:26 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-30  9:47 Martin Liška
2018-12-06  8:26 ` Bernhard Reutner-Fischer [this message]
2018-12-28 18:00   ` Martin Liška

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