From: "Leizhen (ThunderTown)" <thunder.leizhen@huaweicloud.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
Zhen Lei <thunder.leizhen@huawei.com>
Subject: Re: [PATCH 1/2] softirq: fix integer overflow in function show_stat()
Date: Tue, 25 Jul 2023 10:00:38 +0800 [thread overview]
Message-ID: <6e38e31f-4413-1aff-8973-5c3d660bedea@huaweicloud.com> (raw)
In-Reply-To: <ZL6BwiHhvQneJZYH@casper.infradead.org>
On 2023/7/24 21:50, Matthew Wilcox wrote:
> On Mon, Jul 24, 2023 at 09:22:23PM +0800, thunder.leizhen@huaweicloud.com wrote:
>> From: Zhen Lei <thunder.leizhen@huawei.com>
>>
>> The statistics function of softirq is supported by commit aa0ce5bbc2db
>> ("softirq: introduce statistics for softirq") in 2009. At that time,
>> 64-bit processors should not have many cores and would not face
>> significant count overflow problems. Now it's common for a processor to
>> have hundreds of cores. Assume that there are 100 cores and 10
>> TIMER_SOFTIRQ are generated per second, then the 32-bit sum will be
>> overflowed after 50 days.
>
> 50 days is long enough to take a snapshot. You should always be using
> difference between, not absolute values, and understand that they can
> wrap. We only tend to change the size of a counter when it can wrap
> sufficiently quickly that we might miss a wrap (eg tens of seconds).
Yes, I think patch 2/2 can be dropped. I reduced the number of soft
interrupts generated in one second, and actually 100+ or 1000 is normal.
But I think patch 1/2 is necessary. The sum of the output scattered values
does not match the output sum. To solve this problem, we only need to
adjust the type of a local variable.
>
> .
>
--
Regards,
Zhen Lei
next prev parent reply other threads:[~2023-07-25 2:00 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-24 13:22 [PATCH 0/2] softirq: redefine the type of kernel_stat.softirqs[] as unsigned long thunder.leizhen
2023-07-24 13:22 ` [PATCH 1/2] softirq: fix integer overflow in function show_stat() thunder.leizhen
2023-07-24 13:50 ` Matthew Wilcox
2023-07-25 2:00 ` Leizhen (ThunderTown) [this message]
2023-07-25 9:09 ` Leizhen (ThunderTown)
2023-07-25 15:26 ` Matthew Wilcox
2023-07-26 0:59 ` Leizhen (ThunderTown)
2023-07-24 13:22 ` [PATCH 2/2] softirq: redefine the type of kernel_stat.softirqs[] as unsigned long thunder.leizhen
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