Re: [PATCH v2] LoongArch: Correct the calculation logic of thread_count

[Qiang Ma]

在 2025/11/27 17:35, Huacai Chen 写道:
> On Thu, Nov 27, 2025 at 4:56 PM Qiang Ma <maqianga@xxxxxxxxxxxxx> wrote:
> > 在 2025/11/27 15:36, Huacai Chen 写道:
> > > Hi, Qiang,
> > >
> > > On Thu, Nov 27, 2025 at 11:32 AM Qiang Ma <maqianga@xxxxxxxxxxxxx> wrote:
> > > > For thread_count, the current calculation method has a maximum of 255,
> > > > which may not be sufficient in the future. Therefore, we are correcting
> > > > it now.
> > > >
> > > > Reference: SMBIOS Specification, 7.5 Processor Information (Type 4)[1]
> > > >
> > > > [1]: https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.9.0.pdf
> > > >
> > > > Signed-off-by: Qiang Ma <maqianga@xxxxxxxxxxxxx>
> > > > ---
> > > >    arch/loongarch/kernel/setup.c | 9 ++++++++-
> > > >    1 file changed, 8 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> > > > index 25a87378e48e..8dd25fc4bd13 100644
> > > > --- a/arch/loongarch/kernel/setup.c
> > > > +++ b/arch/loongarch/kernel/setup.c
> > > > @@ -56,6 +56,7 @@
> > > >    #define SMBIOS_FREQLOW_MASK            0xFF
> > > >    #define SMBIOS_CORE_PACKAGE_OFFSET     0x23
> > > >    #define SMBIOS_THREAD_PACKAGE_OFFSET   0x25
> > > > +#define SMBIOS_THREAD_PACKAGE_2_OFFSET 0x2E
> > > >    #define LOONGSON_EFI_ENABLE            (1 << 3)
> > > >
> > > >    unsigned long fw_arg0, fw_arg1, fw_arg2;
> > > > @@ -120,13 +121,19 @@ static void __init parse_cpu_table(const struct dmi_header *dm)
> > > >    {
> > > >           long freq_temp = 0;
> > > >           char *dmi_data = (char *)dm;
> > > > +       u8 thread_count;
> > > >
> > > >           freq_temp = ((*(dmi_data + SMBIOS_FREQHIGH_OFFSET) << 8) +
> > > >                           ((*(dmi_data + SMBIOS_FREQLOW_OFFSET)) & SMBIOS_FREQLOW_MASK));
> > > >           cpu_clock_freq = freq_temp * 1000000;
> > > >
> > > >           loongson_sysconf.cpuname = (void *)dmi_string_parse(dm, dmi_data[16]);
> > > > -       loongson_sysconf.cores_per_package = *(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> > > > +       thread_count = *(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> > Yes, this one should need to be converted:
> > thread_count = *(u8 *)(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> > > > +       if (thread_count != 0)
> > > > +               loongson_sysconf.cores_per_package =
> > > > +                               dm->length >= 0x30 && thread_count == 0xFF ?
> > > > +                               *(u16 *)(dmi_data + SMBIOS_THREAD_PACKAGE_2_OFFSET) :
> > > > +                               thread_count;
> > This patch method refers to dmidecode, which is the same as it, like this:
> >
> >                           if (data[0x25] != 0)
> >                                   pr_attr("Thread Count", "%u",
> >                                           h->length >= 0x30 && data[0x25]
> > == 0xFF ?
> >
> >                                           WORD(data + 0x2E) : data[0x25]);
> >
> >
> > > According SPEC, it uses THREAD_COUNT_2 only if dm->length >= 30 and
> > > thread_count == 0xff, so the correct and simplest way is like this:
> > >
> > >           cpu_clock_freq = freq_temp * 1000000;
> > >
> > >           loongson_sysconf.cpuname = (void *)dmi_string_parse(dm, dmi_data[16]);
> > > -       loongson_sysconf.cores_per_package = *(dmi_data +
> > > SMBIOS_THREAD_PACKAGE_OFFSET);
> > > +       if (dm->length < 0x30)
> > > +               thread_count = *(u8 *)(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> > > +       else if (thread_count == 0xff)
> > > +               thread_count = *(u16 *)(dmi_data +
> > > SMBIOS_THREAD_PACKAGE_2_OFFSET);
> > > +       loongson_sysconf.cores_per_package = thread_count;
> > >
> > >           pr_info("CpuClock = %llu\n", cpu_clock_freq);
> > I feel there is a problem with this method.
> > I saw on the 3C6000/Q machine a few days ago that the dm->lenght is 0x30,
> > but only one byte is used, and the thread_count is 128, not 0xFF.
> > Is the initialization thread_count = *(u8 *)(dmi_data +
> > SMBIOS_THREAD_PACKAGE_OFFSET) missing?
> Yes, you are right. Kernel code prefers 0xff rather than 0xFF, and I
I see.
> want to add a comment, so I think the below is OK.
Yes, I also think it's okay. I will update it to v3.
>          loongson_sysconf.cores_per_package = *(u8 *)(dmi_data +
> SMBIOS_THREAD_PACKAGE_OFFSET);
>          if (dm->length >= 0x30 && loongson_sysconf.cores_per_package == 0xff) {
>                  /* SMBIOS 3.0+ has ThreadCount2 for more than 255 threads */
>                  loongson_sysconf.cores_per_package = *(u16 *)(dmi_data
> + SMBIOS_THREAD_PACKAGE_2_OFFSET);
>          }
> Huacai
>
> > Wouldn't it be better to change it this way?
> >
> > +       u8 thread_count;
> >
> >           freq_temp = ((*(dmi_data + SMBIOS_FREQHIGH_OFFSET) << 8) +
> >                           ((*(dmi_data + SMBIOS_FREQLOW_OFFSET)) &
> > SMBIOS_FREQLOW_MASK));
> >           cpu_clock_freq = freq_temp * 1000000;
> >
> >           loongson_sysconf.cpuname = (void *)dmi_string_parse(dm,
> > dmi_data[16]);
> > -       loongson_sysconf.cores_per_package = *(dmi_data +
> > SMBIOS_THREAD_PACKAGE_OFFSET);
> > +       thread_count = *(u8 *)(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> > +       if (thread_count == 0xFF && dm->length >= 0x30)
> > +               thread_count = *(u16 *)(dmi_data +
> > SMBIOS_THREAD_PACKAGE_2_OFFSET);
> > +       loongson_sysconf.cores_per_package = thread_count;
> >
> >           pr_info("CpuClock = %llu\n", cpu_clock_freq);
> >    }
> > > Huacai
> > >
> > > >           pr_info("CpuClock = %llu\n", cpu_clock_freq);
> > > >    }
> > > > --
> > > > 2.20.1