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From: Sven Schnelle <svens@linux.ibm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yinan Liu <yinan@linux.alibaba.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Sachin Sant <sachinp@linux.ibm.com>,
	linuxppc-dev@lists.ozlabs.org,
	Russell King <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org, hca@linux.ibm.com,
	linux-s390@vger.kernel.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: ftrace hangs waiting for rcu
Date: Fri, 28 Jan 2022 17:17:32 +0100	[thread overview]
Message-ID: <yt9da6ffn8bn.fsf@linux.ibm.com> (raw)
In-Reply-To: <YfQVzba5thVs+qap@FVFF77S0Q05N> (Mark Rutland's message of "Fri, 28 Jan 2022 16:11:57 +0000")

Hi Mark,

Mark Rutland <mark.rutland@arm.com> writes:

> On Fri, Jan 28, 2022 at 05:08:48PM +0100, Sven Schnelle wrote:
>> We noticed the PR from Paul and are currently testing the fix. So far
>> it's looking good. The configuration where we have seen the hang is a
>> bit unusual:
>> 
>> - 16 physical CPUs on the kvm host
>> - 248 logical CPUs inside kvm
>
> Aha! 248 is notably *NOT* a power of two, and in this case the shift would be
> wrong (ilog2() would give 7, when we need a shift of 8).
>
> So I suspect you're hitting the same issue as I was.

Argh, indeed! I somehow changed 'power of two' to 'odd number' in my
head. I guess it's time for the weekend. :-)

Thanks!

WARNING: multiple messages have this Message-ID (diff)
From: Sven Schnelle <svens@linux.ibm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-s390@vger.kernel.org, Kees Cook <keescook@chromium.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	hca@linux.ibm.com, LKML <linux-kernel@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	Sachin Sant <sachinp@linux.ibm.com>,
	Russell King <linux@armlinux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yinan Liu <yinan@linux.alibaba.com>,
	linuxppc-dev@lists.ozlabs.org, Ard Biesheuvel <ardb@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: ftrace hangs waiting for rcu
Date: Fri, 28 Jan 2022 17:17:32 +0100	[thread overview]
Message-ID: <yt9da6ffn8bn.fsf@linux.ibm.com> (raw)
In-Reply-To: <YfQVzba5thVs+qap@FVFF77S0Q05N> (Mark Rutland's message of "Fri,  28 Jan 2022 16:11:57 +0000")

Hi Mark,

Mark Rutland <mark.rutland@arm.com> writes:

> On Fri, Jan 28, 2022 at 05:08:48PM +0100, Sven Schnelle wrote:
>> We noticed the PR from Paul and are currently testing the fix. So far
>> it's looking good. The configuration where we have seen the hang is a
>> bit unusual:
>> 
>> - 16 physical CPUs on the kvm host
>> - 248 logical CPUs inside kvm
>
> Aha! 248 is notably *NOT* a power of two, and in this case the shift would be
> wrong (ilog2() would give 7, when we need a shift of 8).
>
> So I suspect you're hitting the same issue as I was.

Argh, indeed! I somehow changed 'power of two' to 'odd number' in my
head. I guess it's time for the weekend. :-)

Thanks!

WARNING: multiple messages have this Message-ID (diff)
From: Sven Schnelle <svens@linux.ibm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yinan Liu <yinan@linux.alibaba.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Sachin Sant <sachinp@linux.ibm.com>,
	linuxppc-dev@lists.ozlabs.org,
	Russell King <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org, hca@linux.ibm.com,
	linux-s390@vger.kernel.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: ftrace hangs waiting for rcu
Date: Fri, 28 Jan 2022 17:17:32 +0100	[thread overview]
Message-ID: <yt9da6ffn8bn.fsf@linux.ibm.com> (raw)
In-Reply-To: <YfQVzba5thVs+qap@FVFF77S0Q05N> (Mark Rutland's message of "Fri,  28 Jan 2022 16:11:57 +0000")

Hi Mark,

Mark Rutland <mark.rutland@arm.com> writes:

> On Fri, Jan 28, 2022 at 05:08:48PM +0100, Sven Schnelle wrote:
>> We noticed the PR from Paul and are currently testing the fix. So far
>> it's looking good. The configuration where we have seen the hang is a
>> bit unusual:
>> 
>> - 16 physical CPUs on the kvm host
>> - 248 logical CPUs inside kvm
>
> Aha! 248 is notably *NOT* a power of two, and in this case the shift would be
> wrong (ilog2() would give 7, when we need a shift of 8).
>
> So I suspect you're hitting the same issue as I was.

Argh, indeed! I somehow changed 'power of two' to 'odd number' in my
head. I guess it's time for the weekend. :-)

Thanks!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2022-01-28 16:18 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-27 16:42 [PATCH] ftrace: Have architectures opt-in for mcount build time sorting Steven Rostedt
2022-01-27 16:42 ` Steven Rostedt
2022-01-27 16:42 ` Steven Rostedt
2022-01-27 18:23 ` Mark Rutland
2022-01-27 18:23   ` Mark Rutland
2022-01-27 18:23   ` Mark Rutland
2022-01-27 18:42   ` ftrace hangs waiting for rcu (was: Re: [PATCH] ftrace: Have architectures opt-in for mcount build time sorting) Sven Schnelle
2022-01-27 18:42     ` Sven Schnelle
2022-01-27 18:42     ` Sven Schnelle
2022-01-28 15:42     ` Mark Rutland
2022-01-28 15:42       ` Mark Rutland
2022-01-28 15:42       ` Mark Rutland
2022-01-28 16:08       ` ftrace hangs waiting for rcu Sven Schnelle
2022-01-28 16:08         ` Sven Schnelle
2022-01-28 16:08         ` Sven Schnelle
2022-01-28 16:11         ` Mark Rutland
2022-01-28 16:11           ` Mark Rutland
2022-01-28 16:11           ` Mark Rutland
2022-01-28 16:15           ` Paul E. McKenney
2022-01-28 16:15             ` Paul E. McKenney
2022-01-28 16:15             ` Paul E. McKenney
2022-01-28 17:47             ` Paul E. McKenney
2022-01-28 17:47               ` Paul E. McKenney
2022-01-28 17:47               ` Paul E. McKenney
2022-01-28 16:17           ` Sven Schnelle [this message]
2022-01-28 16:17             ` Sven Schnelle
2022-01-28 16:17             ` Sven Schnelle
2022-01-28 21:11 ` [PATCH] ftrace: Have architectures opt-in for mcount build time sorting Joe Lawrence
2022-01-28 21:11   ` Joe Lawrence
2022-01-28 21:11   ` Joe Lawrence
2022-01-28 21:39   ` Steven Rostedt
2022-01-28 21:39     ` Steven Rostedt
2022-01-28 21:39     ` Steven Rostedt

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