From: Ingo Molnar <mingo@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Len Brown <lenb@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
x86@kernel.org, linux-pm@vger.kernel.org,
Robin Jarry <rjarry@redhat.com>, Joe Mario <jmario@redhat.com>,
Randy Dunlap <rdunlap@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v6 0/4] x86/speculation: Disable IBRS when idle
Date: Wed, 4 Oct 2023 13:50:16 +0200 [thread overview]
Message-ID: <ZR1RePXx6/zZueI8@gmail.com> (raw)
In-Reply-To: <20230727184600.26768-1-longman@redhat.com>
* Waiman Long <longman@redhat.com> wrote:
> For Intel processors that need to turn on IBRS to protect against
> Spectre v2 and Retbleed, the IBRS bit in the SPEC_CTRL MSR affects
> the performance of the whole core even if only one thread is turning
> it on when running in the kernel. For user space heavy applications,
> the performance impact of occasionally turning IBRS on during syscalls
> shouldn't be significant. Unfortunately, that is not the case when the
> sibling thread is idling in the kernel. In that case, the performance
> impact can be significant.
>
> When DPDK is running on an isolated CPU thread processing network packets
> in user space while its sibling thread is idle. The performance of the
> busy DPDK thread with IBRS on and off in the sibling idle thread are:
>
> IBRS on IBRS off
> ------- --------
> packets/second: 7.8M 10.4M
> avg tsc cycles/packet: 282.26 209.86
>
> This is a 25% performance degradation. The test system is a Intel Xeon
> 4114 CPU @ 2.20GHz.
Ok, that's a solid improvement, and the feature has no obvious
downsides, so I've applied your series to tip:sched/core with a few
edits here and there.
Thanks!
Ingo
next prev parent reply other threads:[~2023-10-04 11:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-27 18:45 [PATCH v6 0/4] x86/speculation: Disable IBRS when idle Waiman Long
2023-07-27 18:45 ` [PATCH v6 1/4] x86/speculation: Add __update_spec_ctrl() helper Waiman Long
2023-07-27 18:45 ` [PATCH v6 2/4] x86/idle: Disable IBRS when cpu is offline Waiman Long
2023-07-27 18:45 ` [PATCH v6 3/4] intel_idle: Use __update_spec_ctrl() in intel_idle_ibrs() Waiman Long
2023-07-27 18:46 ` [PATCH v6 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS Waiman Long
2023-08-16 20:42 ` [PATCH v6 0/4] x86/speculation: Disable IBRS when idle Waiman Long
2023-10-04 11:50 ` Ingo Molnar [this message]
2023-10-04 16:11 ` Waiman Long
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