From: Peter Zijlstra <peterz@infradead.org>
To: Artem Bityutskiy <dedekind1@gmail.com>
Cc: x86@kernel.org, Linux PM Mailing List <linux-pm@vger.kernel.org>
Subject: Re: [PATCH 1/3] x86/mwait: Add support for idle via umwait
Date: Mon, 6 Mar 2023 15:55:24 +0100 [thread overview]
Message-ID: <20230306145524.GF1267364@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230306123418.720679-2-dedekind1@gmail.com>
On Mon, Mar 06, 2023 at 02:34:16PM +0200, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
>
> On Intel platforms, C-states are requested using the 'monitor/mwait'
> instructions pair, as implemented in 'mwait_idle_with_hints()'. This
> mechanism allows for entering C1 and deeper C-states.
>
> Sapphire Rapids Xeon supports new idle states - C0.1 and C0.2 (later C0.x).
> These idle states have lower latency comparing to C1, and can be requested
> with either 'tpause' and 'umwait' instructions.
>
> Linux already uses the 'tpause' instruction in delay functions like
> 'udelay()'. This patch adds 'umwait' and 'umonitor' instructions support.
>
> 'umwait' and 'tpause' instructions are very similar - both send the CPU to
> C0.x and have the same break out rules. But unlike 'tpause', 'umwait' works
> together with 'umonitor' and exits the C0.x when the monitored memory
> address is modified (similar idea as with 'monitor/mwait').
>
> This patch implements the 'umwait_idle()' function, which works very
> similarly to existing 'mwait_idle_with_hints()', but requests C0.x. The
> intention is to use it from the 'intel_idle' driver.
Still wondering wth regular mwait can't access these new idle states.
next prev parent reply other threads:[~2023-03-06 14:56 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 12:34 [PATCH 0/3] Sapphire Rapids C0.x idle states support Artem Bityutskiy
2023-03-06 12:34 ` [PATCH 1/3] x86/mwait: Add support for idle via umwait Artem Bityutskiy
2023-03-06 14:55 ` Peter Zijlstra [this message]
2023-03-07 11:55 ` Rafael J. Wysocki
2023-03-08 12:35 ` Peter Zijlstra
2023-03-06 12:34 ` [PATCH 2/3] x86/umwait: Increase tpause and umwait quanta Artem Bityutskiy
2023-03-06 12:34 ` [PATCH 3/3] intel_idle: add C0.2 state for Sapphire Rapids Xeon Artem Bityutskiy
2023-03-06 15:32 ` Peter Zijlstra
2023-03-07 12:39 ` Rafael J. Wysocki
2023-03-08 12:32 ` Peter Zijlstra
2023-03-09 8:01 ` Artem Bityutskiy
2023-03-14 12:24 ` Peter Zijlstra
2023-03-17 8:42 ` Artem Bityutskiy
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