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From: Peter Zijlstra <peterz@infradead.org>
To: Ganapatrao Prabhakerrao Kulkarni <gkulkarni@marvell.com>
Cc: "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"will@kernel.org" <will@kernel.org>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"gklkml16@gmail.com" <gklkml16@gmail.com>
Subject: Re: [PATCH 1/2] perf/core: Adding capability to disable PMUs event multiplexing
Date: Wed, 6 Nov 2019 10:58:10 +0100	[thread overview]
Message-ID: <20191106095810.GK5671@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191106094032.GV4131@hirez.programming.kicks-ass.net>

On Wed, Nov 06, 2019 at 10:40:32AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 06, 2019 at 01:01:40AM +0000, Ganapatrao Prabhakerrao Kulkarni wrote:
> > When PMUs are registered, perf core enables event multiplexing
> > support by default. There is no provision for PMUs to disable
> > event multiplexing, if PMUs want to disable due to unavoidable
> > circumstances like hardware errata etc.
> > 
> > Adding PMU capability flag PERF_PMU_CAP_NO_MUX_EVENTS and support
> > to allow PMUs to explicitly disable event multiplexing.
> 
> This doesn't make sense, multiplexing relies on nothing that normal
> event scheduling doesn't also rely on.
> 
> Either you can schedule different sets of events, or you cannot.

More specifically, how is a reschedule due to rotation any different
than a reschedule due to context switch?

Both cases we do a full reprogram of the PMU.

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Ganapatrao Prabhakerrao Kulkarni <gkulkarni@marvell.com>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"gklkml16@gmail.com" <gklkml16@gmail.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"will@kernel.org" <will@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/2] perf/core: Adding capability to disable PMUs event multiplexing
Date: Wed, 6 Nov 2019 10:58:10 +0100	[thread overview]
Message-ID: <20191106095810.GK5671@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191106094032.GV4131@hirez.programming.kicks-ass.net>

On Wed, Nov 06, 2019 at 10:40:32AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 06, 2019 at 01:01:40AM +0000, Ganapatrao Prabhakerrao Kulkarni wrote:
> > When PMUs are registered, perf core enables event multiplexing
> > support by default. There is no provision for PMUs to disable
> > event multiplexing, if PMUs want to disable due to unavoidable
> > circumstances like hardware errata etc.
> > 
> > Adding PMU capability flag PERF_PMU_CAP_NO_MUX_EVENTS and support
> > to allow PMUs to explicitly disable event multiplexing.
> 
> This doesn't make sense, multiplexing relies on nothing that normal
> event scheduling doesn't also rely on.
> 
> Either you can schedule different sets of events, or you cannot.

More specifically, how is a reschedule due to rotation any different
than a reschedule due to context switch?

Both cases we do a full reprogram of the PMU.

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  reply	other threads:[~2019-11-06  9:58 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-06  1:01 [PATCH 0/2] Workaround for ThunderX2 erratum 221 Ganapatrao Prabhakerrao Kulkarni
2019-11-06  1:01 ` Ganapatrao Prabhakerrao Kulkarni
2019-11-06  1:01 ` [PATCH 1/2] perf/core: Adding capability to disable PMUs event multiplexing Ganapatrao Prabhakerrao Kulkarni
2019-11-06  1:01   ` Ganapatrao Prabhakerrao Kulkarni
2019-11-06  9:40   ` Peter Zijlstra
2019-11-06  9:40     ` Peter Zijlstra
2019-11-06  9:58     ` Peter Zijlstra [this message]
2019-11-06  9:58       ` Peter Zijlstra
2019-11-06 11:28   ` Mark Rutland
2019-11-06 11:28     ` Mark Rutland
2019-11-06 23:28     ` Ganapatrao Kulkarni
2019-11-06 23:28       ` Ganapatrao Kulkarni
2019-11-07 14:35       ` Ganapatrao Kulkarni
2019-11-07 14:35         ` Ganapatrao Kulkarni
2019-11-07 14:52       ` Mark Rutland
2019-11-07 14:52         ` Mark Rutland
2019-11-07 15:45         ` Ganapatrao Kulkarni
2019-11-07 15:45           ` Ganapatrao Kulkarni
2019-11-07 15:54           ` Mark Rutland
2019-11-07 15:54             ` Mark Rutland
2019-11-07 15:04       ` Peter Zijlstra
2019-11-07 15:04         ` Peter Zijlstra
2019-11-07 23:17   ` kbuild test robot
2019-11-07 23:17     ` kbuild test robot
2019-11-07 23:17     ` kbuild test robot
2019-11-06  1:01 ` [PATCH 2/2] Thunderx2, uncore: Add workaround for ThunderX2 erratum 221 Ganapatrao Prabhakerrao Kulkarni
2019-11-06  1:01   ` Ganapatrao Prabhakerrao Kulkarni
2019-11-06 11:37   ` Mark Rutland
2019-11-06 11:37     ` Mark Rutland

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