From: Mark Rutland <mark.rutland@arm.com>
To: He Ying <heying24@huawei.com>
Cc: catalin.marinas@arm.com, dvyukov@google.com, elver@google.com,
james.morse@arm.com, linux-arm-kernel@lists.infradead.org,
paulmck@kernel.org, peterz@infradead.org, will@kernel.org
Subject: Re: [PATCHv2 06/11] arm64: entry: move el1 irq/nmi logic to C
Date: Thu, 6 May 2021 10:16:37 +0100 [thread overview]
Message-ID: <20210506091637.GC12883@C02TD0UTHF1T.local> (raw)
In-Reply-To: <a344dbaa-50da-47e6-5d03-8a76c5c67c92@huawei.com>
On Thu, May 06, 2021 at 04:28:09PM +0800, He Ying wrote:
> Hi Mark,
Hi,
> I have faced a performance regression for handling IPIs since this commit.
>
> I caculate the cycles from the entry of el1_irq to the entry of
> gic_handle_irq.
>
> From my test, this commit may overhead an average of 200 cycles. Do you
>
> have any ideas about this? Looking forward to your reply.
On that path, the only meaningfull difference is the call to
enter_el1_irq_or_nmi(), since that's now unconditional, and it's an
extra layer in the callchain.
When either CONFIG_ARM64_PSEUDO_NMI or CONFIG_TRACE_IRQFLAGS are
selected, enter_el1_irq_or_nmi() is a wrapper for functions we'd already
call, and I'd expectthe cost of the callees to dominate.
When neither CONFIG_ARM64_PSEUDO_NMI nor CONFIG_TRACE_IRQFLAGS are
selected, this should add a trivial function that immediately returns,
and so 200 cycles seems excessive.
Building that commit with defconfig, I see that GCC 10.1.0 generates:
| ffff800010dfc864 <enter_el1_irq_or_nmi>:
| ffff800010dfc864: d503233f paciasp
| ffff800010dfc868: d50323bf autiasp
| ffff800010dfc86c: d65f03c0 ret
... so perhaps the PACIASP and AUTIASP have an impact?
I have a few questions:
* Which CPU do you see this on?
* Does that CPU implement pointer authentication?
* What kernel config are you using? e.g. is this seen with defconfig?
* What's the total cycle count from el1_irq to gic_handle_irq?
* Does this measurably impact a real workload?
Thanks,
Mark.
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next prev parent reply other threads:[~2021-05-06 9:20 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-30 11:59 [PATCHv2 00/11] arm64: entry lockdep/rcu/tracing fixes Mark Rutland
2020-11-30 11:59 ` [PATCHv2 01/11] arm64: syscall: exit userspace before unmasking exceptions Mark Rutland
2020-11-30 11:59 ` [PATCHv2 02/11] arm64: mark idle code as noinstr Mark Rutland
2020-11-30 11:59 ` [PATCHv2 03/11] arm64: entry: mark entry " Mark Rutland
2020-11-30 11:59 ` [PATCHv2 04/11] arm64: entry: move enter_from_user_mode to entry-common.c Mark Rutland
2020-11-30 11:59 ` [PATCHv2 05/11] arm64: entry: prepare ret_to_user for function call Mark Rutland
2020-12-17 17:57 ` Guenter Roeck
2020-12-17 18:38 ` Catalin Marinas
2020-11-30 11:59 ` [PATCHv2 06/11] arm64: entry: move el1 irq/nmi logic to C Mark Rutland
2021-05-06 8:28 ` He Ying
2021-05-06 9:16 ` Mark Rutland [this message]
[not found] ` <e3843e03-173e-10a6-5b14-0d8c14219e09@huawei.com>
2021-05-06 10:58 ` Mark Rutland
2021-05-07 3:25 ` He Ying
2021-05-07 9:41 ` Mark Rutland
2021-05-07 10:02 ` He Ying
2020-11-30 11:59 ` [PATCHv2 07/11] arm64: entry: fix non-NMI user<->kernel transitions Mark Rutland
2020-11-30 11:59 ` [PATCHv2 08/11] arm64: ptrace: prepare for EL1 irq/rcu tracking Mark Rutland
2020-11-30 11:59 ` [PATCHv2 09/11] arm64: entry: fix non-NMI kernel<->kernel transitions Mark Rutland
2021-04-25 5:29 ` Zenghui Yu
2021-04-26 9:21 ` Mark Rutland
2021-04-26 13:39 ` Zenghui Yu
2021-04-27 7:15 ` Zenghui Yu
2021-04-27 14:43 ` Mark Rutland
2020-11-30 11:59 ` [PATCHv2 10/11] arm64: entry: fix NMI {user, kernel}->kernel transitions Mark Rutland
2020-11-30 11:59 ` [PATCHv2 11/11] arm64: entry: fix EL1 debug transitions Mark Rutland
2020-11-30 13:52 ` [PATCHv2 00/11] arm64: entry lockdep/rcu/tracing fixes Will Deacon
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