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From: Thomas Gleixner <tglx@linutronix.de>
To: "Yang, WenYou" <WenYou.Yang@amd.com>,
	Peter Zijlstra <peterz@infradead.org>
Cc: "Phillips, Kim" <kim.phillips@amd.com>,
	"Li, Ying" <YING.LI@amd.com>, "Pan, Xinhui" <Xinhui.Pan@amd.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
	"jpoimboe@kernel.org" <jpoimboe@kernel.org>,
	"gpiccoli@igalia.com" <gpiccoli@igalia.com>,
	"Yuan, Perry" <Perry.Yuan@amd.com>, "bp@alien8.de" <bp@alien8.de>,
	"Limonciello, Mario" <Mario.Limonciello@amd.com>,
	"Deucher, Alexander" <Alexander.Deucher@amd.com>,
	"Quan,  Evan" <Evan.Quan@amd.com>,
	"Koenig, Christian" <Christian.Koenig@amd.com>,
	"Liang, Richard qi" <Richardqi.Liang@amd.com>,
	"Liu, Kun" <Kun.Liu2@amd.com>
Subject: RE: [PATCH v3 1/2] cpu/smt: add a notifier to notify the SMT changes
Date: Fri, 31 Mar 2023 23:52:50 +0200	[thread overview]
Message-ID: <87pm8osi4t.ffs@tglx> (raw)
In-Reply-To: <DM6PR12MB3531340547BE346D07E88BE3FD8F9@DM6PR12MB3531.namprd12.prod.outlook.com>

On Fri, Mar 31 2023 at 05:49, WenYou Yang wrote:

<SNIP>
        Removing pointlessly copied mail headers. Please fix your email
        client
</SNIP>

>> >
>> > So what do you want to have happen when someone goes and manually
>> > offlines all the SMT siblings using
>> > /sys/devices/system/cpu/cpu*/online
>> > ?
>> 
>> I don't consider this situation.  Any suggestions will be deeply appreciated.
>
> Hi Peter,
>
> I don't find a good method to handle this situation.
> Yes, manually offlining all the SMT sibling will get the same result of SMT disabling on the fly.
>
> Actually, the normal way to enable/disable SMT on the fly is to echo on/off > /sys/device/system/cpu/smt/control

That's the most convenient way, right.

But why do we need a kernel notifier for this, if you can do the same
with a sysfs knob for your driver?

Then user space can fiddle with SMT control in sysfs and afterwards tell
the driver that it should reconfigure.

That makes a ton more sense than this random notifier.

Thanks,

        tglx

WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: "Yang, WenYou" <WenYou.Yang@amd.com>,
	Peter Zijlstra <peterz@infradead.org>
Cc: "Deucher, Alexander" <Alexander.Deucher@amd.com>,
	"Koenig, Christian" <Christian.Koenig@amd.com>,
	"Pan, Xinhui" <Xinhui.Pan@amd.com>,
	"Quan, Evan" <Evan.Quan@amd.com>,
	"Limonciello, Mario" <Mario.Limonciello@amd.com>,
	"bp@alien8.de" <bp@alien8.de>,
	"jpoimboe@kernel.org" <jpoimboe@kernel.org>,
	"Phillips, Kim" <kim.phillips@amd.com>,
	"Yuan, Perry" <Perry.Yuan@amd.com>,
	"Liang, Richard qi" <Richardqi.Liang@amd.com>,
	"Li, Ying" <YING.LI@amd.com>, "Liu, Kun" <Kun.Liu2@amd.com>,
	"gpiccoli@igalia.com" <gpiccoli@igalia.com>,
	"amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v3 1/2] cpu/smt: add a notifier to notify the SMT changes
Date: Fri, 31 Mar 2023 23:52:50 +0200	[thread overview]
Message-ID: <87pm8osi4t.ffs@tglx> (raw)
In-Reply-To: <DM6PR12MB3531340547BE346D07E88BE3FD8F9@DM6PR12MB3531.namprd12.prod.outlook.com>

On Fri, Mar 31 2023 at 05:49, WenYou Yang wrote:

<SNIP>
        Removing pointlessly copied mail headers. Please fix your email
        client
</SNIP>

>> >
>> > So what do you want to have happen when someone goes and manually
>> > offlines all the SMT siblings using
>> > /sys/devices/system/cpu/cpu*/online
>> > ?
>> 
>> I don't consider this situation.  Any suggestions will be deeply appreciated.
>
> Hi Peter,
>
> I don't find a good method to handle this situation.
> Yes, manually offlining all the SMT sibling will get the same result of SMT disabling on the fly.
>
> Actually, the normal way to enable/disable SMT on the fly is to echo on/off > /sys/device/system/cpu/smt/control

That's the most convenient way, right.

But why do we need a kernel notifier for this, if you can do the same
with a sysfs knob for your driver?

Then user space can fiddle with SMT control in sysfs and afterwards tell
the driver that it should reconfigure.

That makes a ton more sense than this random notifier.

Thanks,

        tglx

  reply	other threads:[~2023-03-31 22:21 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-29  1:51 [PATCH v3 0/2] send message to pmfw when SMT changes Wenyou Yang
2023-03-29  1:51 ` Wenyou Yang
2023-03-29  1:51 ` [PATCH v3 1/2] cpu/smt: add a notifier to notify the " Wenyou Yang
2023-03-29  1:51   ` Wenyou Yang
2023-03-29  7:10   ` Peter Zijlstra
2023-03-29  7:10     ` Peter Zijlstra
2023-03-29  7:23     ` Yang, WenYou
2023-03-29  7:23       ` Yang, WenYou
2023-03-29  8:50       ` Peter Zijlstra
2023-03-29  8:50         ` Peter Zijlstra
2023-03-29  9:43         ` Yang, WenYou
2023-03-29  9:43           ` Yang, WenYou
2023-03-31  5:49           ` Yang, WenYou
2023-03-31  5:49             ` Yang, WenYou
2023-03-31 21:52             ` Thomas Gleixner [this message]
2023-03-31 21:52               ` Thomas Gleixner
2023-03-29  1:51 ` [PATCH v3 2/2] drm/amd/pm: vangogh: send the SMT enable message to pmfw Wenyou Yang
2023-03-29  1:51   ` Wenyou Yang
2023-03-29  4:18   ` Mario Limonciello
2023-03-29  4:18     ` Mario Limonciello
2023-03-29  7:26     ` Yang, WenYou
2023-03-29  7:26       ` Yang, WenYou
2023-03-29  6:15   ` Lazar, Lijo
2023-03-29  6:15     ` Lazar, Lijo
2023-03-29  7:25     ` Yang, WenYou
2023-03-29  7:25       ` Yang, WenYou

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