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Message-ID: <663229c2-1957-2af5-678c-5d553507f5f3@intel.com>
Date: Fri, 2 Jul 2021 07:49:01 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Yaohui Wang <yaohuiwang@...ux.alibaba.com>, tglx@...utronix.de
Cc: luto@...nel.org, peterz@...radead.org, mingo@...hat.com,
bp@...en8.de, x86@...nel.org, linux-kernel@...r.kernel.org,
luoben@...ux.alibaba.com, Tom Lendacky <thomas.lendacky@....com>,
Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v3 1/2] x86/ioremap: fix the pfn calculation mistake in
__ioremap_check_ram()
On 7/2/21 3:05 AM, Yaohui Wang wrote:
> On 2021/7/1 22:41, Dave Hansen wrote:
>> Was this issue found by inspection, or is it causing an actual problem
>> in practice?
>
> This issus truly caused terrible perforamnce downgrade in the practice.
> When developing an out of tree module in our testing environment,
> invoking ioremap() on normal RAM causes apparent CLI lag. The Unixbench
> score also decreases a lot (5x slowdown in the worst case).
>
> Debugging such performance issue is extremely difficult, especially when
> the code of the faulty module itself is already very complex. I tested
> the system in many aspects before finally located this problem.
Do you know why this check:
> if ((res->flags & IORESOURCE_SYSTEM_RAM) != IORESOURCE_SYSTEM_RAM)
> return false;
did not catch your out-of-tree driver's errant ioremap()?
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