From: "Robin Jarry" <rjarry@redhat.com>
To: "Waiman Long" <longman@redhat.com>,
"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>,
Peter Zijlstra <peterz@infradead.org> ,
Josh Poimboeuf <jpoimboe@kernel.org>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider" <vschneid@redhat.com>
Cc: <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
"Joe Mario" <jmario@redhat.com>
Subject: Re: [PATCH 0/5] x86/speculation: Disable IBRS when idle
Date: Fri, 16 Jun 2023 22:14:52 +0200 [thread overview]
Message-ID: <CTECMFWMMST3.9FTWRDG7FFKQ@ringo> (raw)
In-Reply-To: <20230616200003.745742-1-longman@redhat.com>
Waiman Long, Jun 16, 2023 at 21:59:
> 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.
>
> This patch series turns off IBRS when in various idle mode to eliminate
> the performance impact of the idling thread on its busy sibling thread.
Hi Longman,
thanks a lot for the quick turnaround on this issue.
Tested-by: Robin Jarry <rjarry@redhat.com>
next parent reply other threads:[~2023-06-16 20:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230616200003.745742-1-longman@redhat.com>
2023-06-16 20:14 ` Robin Jarry [this message]
2023-06-17 12:21 ` [PATCH 0/5] x86/speculation: Disable IBRS when idle Peter Zijlstra
2023-06-17 16:13 ` Robin Jarry
2023-06-19 1:18 ` Waiman Long
2023-06-19 3:25 ` Waiman Long
2023-06-19 8:47 ` Peter Zijlstra
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