Re: [PATCH v4] ACPI: processor_idle: Fix invalid comparison with insertion sort for latency

[Mario Limonciello <mario.limonciello@xxxxxxx>]

On 7/2/2024 2:28, Julian Sikorski wrote:
> Am 01.07.24 um 22:56 schrieb Kuan-Wei Chiu:
> > The acpi_cst_latency_cmp comparison function currently used for sorting
> > C-state latencies does not satisfy transitivity, causing incorrect
> > sorting results. Specifically, if there are two valid acpi_processor_cx
> > elements A and B and one invalid element C, it may occur that A < B,
> > A = C, and B = C. Sorting algorithms assume that if A < B and A = C,
> > then C < B, leading to incorrect ordering.
> >
> > Given the small size of the array (<=8), we replace the library sort
> > function with a simple insertion sort that properly ignores invalid
> > elements and sorts valid ones based on latency. This change ensures
> > correct ordering of the C-state latencies.
> >
> > Fixes: 65ea8f2c6e23 ("ACPI: processor idle: Fix up C-state latency if 
> > not ordered")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reported-by: Julian Sikorski <belegdol@xxxxxxxxx>
> > Closes: 
> > https://lore.kernel.org/lkml/70674dc7-5586-4183-8953-8095567e73df@xxxxxxxxx/
> > Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
> > ---
> > v3 -> v4:
> > - Rename the parameter 'arr' to 'states'.
> > - Add empty lines to enhance readability.
> >
> > Note: I only performed a build test and a simple unit test to ensure
> >        the latency of valid elements is correctly sorted in the randomly
> >        generated data.
>
> Hello,
>
> thanks for the patch. I have tested this applied on top of Fedora 6.9.7 
> kernel on my Asus laptop and the message about suspend not reaching the 
> deepest state is gone. Thank you.

That's great news.

> I wonder whether this will also fix random S3 suspend issues I have been 
> seeing on my 5600x since 6.9 kernel too. I will definitely try.

Does your 5600x also sort C states?  You'll see message in the logs.  If 
so yes it could help.  If not; you probably will need to bisect that 
separately.

> Best regards,
> Julian
>
> Tested-by: Julian Sikorski <belegdol@xxxxxxxxx>
>
> >   drivers/acpi/processor_idle.c | 37 +++++++++++++++--------------------
> >   1 file changed, 16 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/acpi/processor_idle.c 
> > b/drivers/acpi/processor_idle.c
> > index bd6a7857ce05..831fa4a12159 100644
> > --- a/drivers/acpi/processor_idle.c
> > +++ b/drivers/acpi/processor_idle.c
> > @@ -16,7 +16,6 @@
> >   #include <linux/acpi.h>
> >   #include <linux/dmi.h>
> >   #include <linux/sched.h>       /* need_resched() */
> > -#include <linux/sort.h>
> >   #include <linux/tick.h>
> >   #include <linux/cpuidle.h>
> >   #include <linux/cpu.h>
> > @@ -386,25 +385,24 @@ static void 
> > acpi_processor_power_verify_c3(struct acpi_processor *pr,
> >       acpi_write_bit_register(ACPI_BITREG_BUS_MASTER_RLD, 1);
> >   }
> > -static int acpi_cst_latency_cmp(const void *a, const void *b)
> > +static void acpi_cst_latency_sort(struct acpi_processor_cx *states, 
> > size_t length)
> >   {
> > -    const struct acpi_processor_cx *x = a, *y = b;
> > +    int i, j, k;
> > -    if (!(x->valid && y->valid))
> > -        return 0;
> > -    if (x->latency > y->latency)
> > -        return 1;
> > -    if (x->latency < y->latency)
> > -        return -1;
> > -    return 0;
> > -}
> > -static void acpi_cst_latency_swap(void *a, void *b, int n)
> > -{
> > -    struct acpi_processor_cx *x = a, *y = b;
> > +    for (i = 1; i < length; i++) {
> > +        if (!states[i].valid)
> > +            continue;
> > -    if (!(x->valid && y->valid))
> > -        return;
> > -    swap(x->latency, y->latency);
> > +        for (j = i - 1, k = i; j >= 0; j--) {
> > +            if (!states[j].valid)
> > +                continue;
> > +
> > +            if (states[j].latency > states[k].latency)
> > +                swap(states[j].latency, states[k].latency);
> > +
> > +            k = j;
> > +        }
> > +    }
> >   }
> >   static int acpi_processor_power_verify(struct acpi_processor *pr)
> > @@ -449,10 +447,7 @@ static int acpi_processor_power_verify(struct 
> > acpi_processor *pr)
> >       if (buggy_latency) {
> >           pr_notice("FW issue: working around C-state latencies out of 
> > order\n");
> > -        sort(&pr->power.states[1], max_cstate,
> > -             sizeof(struct acpi_processor_cx),
> > -             acpi_cst_latency_cmp,
> > -             acpi_cst_latency_swap);
> > +        acpi_cst_latency_sort(&pr->power.states[1], max_cstate);
> >       }
> >       lapic_timer_propagate_broadcast(pr);