Messages in this thread | | | Subject | Re: [PATCH v3 1/2] x86/ioremap: fix the pfn calculation mistake in __ioremap_check_ram() | From | Dave Hansen <> | Date | Fri, 2 Jul 2021 07:49:01 -0700 |
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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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