Re: [PATCH v2 17/23] x86/resctrl: Abstract __rmid_read()

[Reinette Chatre]

Hi Babu,

On 10/20/2021 12:22 PM, Babu Moger wrote:
> On 10/20/21 1:15 PM, Reinette Chatre wrote:
> > On 10/19/2021 4:20 PM, Babu Moger wrote:
> > > On 10/1/21 11:02 AM, James Morse wrote:
> > > > __rmid_read() selects the specified eventid and returns the counter
> > > > value from the msr. The error handling is architecture specific, and
> > > > handled by the callers, rdtgroup_mondata_show() and __mon_event_count().
> > > >
> > > > Error handling should be handled by architecture specific code, as
> > > > a different architecture may have different requirements. MPAM's
> > > > counters can report that they are 'not ready', requiring a second
> > > > read after a short delay. This should be hidden from resctrl.
> > > >
> > > > Make __rmid_read() the architecture specific function for reading
> > > > a counter. Rename it resctrl_arch_rmid_read() and move the error
> > > > handling into it.
> > > >
> > > > Signed-off-by: James Morse <james.morse@xxxxxxx>
> > > > ---
> > > > Changes since v1:
> > > >    * Return EINVAL from the impossible case in __mon_event_count() instead
> > > >      of an x86 hardware specific value.
> > > > ---
> > > >    arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  4 +--
> > > >    arch/x86/kernel/cpu/resctrl/internal.h    |  2 +-
> > > >    arch/x86/kernel/cpu/resctrl/monitor.c     | 42 +++++++++++++++--------
> > > >    include/linux/resctrl.h                   |  1 +
> > > >    4 files changed, 31 insertions(+), 18 deletions(-)
> > > >
> > > > diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> > > > b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> > > > index 25baacd331e0..c8ca7184c6d9 100644
> > > > --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> > > > +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> > > > @@ -579,9 +579,9 @@ int rdtgroup_mondata_show(struct seq_file *m, void
> > > > *arg)
> > > >          mon_event_read(&rr, r, d, rdtgrp, evtid, false);
> > > >    -    if (rr.val & RMID_VAL_ERROR)
> > > > +    if (rr.err == -EIO)
> > > >            seq_puts(m, "Error\n");
> > > > -    else if (rr.val & RMID_VAL_UNAVAIL)
> > > > +    else if (rr.err == -EINVAL)
> > > >            seq_puts(m, "Unavailable\n");
> > > >        else
> > > >            seq_printf(m, "%llu\n", rr.val * hw_res->mon_scale);
> > >
> > > This patch breaks the earlier fix
> > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2Fcommit%2F%3Fh%3Dv5.15-rc6%26id%3D064855a69003c24bd6b473b367d364e418c57625&amp;data=04%7C01%7Cbabu.moger%40amd.com%7C85219a5827114935cdaa08d993f59fa0%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637703505420472920%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=yP8awDgGGZ%2BWj5ZItdTNJItTVuK828yGnibwq%2BrVaf0%3D&amp;reserved=0
> > >
> > >
> > > When the user reads the events on the default monitoring group with
> > > multiple subgroups, the events on all subgroups are consolidated
> > > together. In case if the last rmid read was resulted in error then whole
> > > group will be reported as error. The err field needs to be cleared.
> > >
> > > Please add this patch to clear the error.
> > >
> > > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> > > b/arch/x86/kernel/cpu/resctrl/monitor.c
> > > index 14bc843043da..0e4addf237ec 100644
> > > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > > @@ -444,6 +444,8 @@ void mon_event_count(void *info)
> > >           /* Report error if none of rmid_reads are successful */
> > >           if (ret_val)
> > >                   rr->val = ret_val;
> > > +       else
> > > +               rr->err  = 0;
> > >    }
> > >
> > >    /*
> >
> > Good catch, thank you.
> >
> > Even so, I do not think mon_event_count()'s usage of __mon_event_count()
> > was taken into account by this patch and needs a bigger rework than the
> > above fixup. For example, if I understand correctly ret_val is the error
> > and rr->val no longer expected to contain the error after this patch. So
> > keeping that assignment to rr->val is not correct.
>
> Yes. You are right. rr->val is not expected to contain the error.
> Hopefully, this should help.
>
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 14bc843043da..105d972cc511 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -441,9 +441,9 @@ void mon_event_count(void *info)
>                  }
>          }
>
> -       /* Report error if none of rmid_reads are successful */
> -       if (ret_val)
> -               rr->val = ret_val;
> +       /* Clear the error if at least one of the rmid reads succeed */
> +       if (ret_val == 0)
> +               rr->err = 0;
>   }
>
>   /*

Yes, this looks good. If the first __mon_event_count() succeeds but a 
following one fails then the data still needs to be reported so the 
error code needs to be fixed up afterwards and cannot be done inside 
__mon_event_count(). Thank you very much.

Reinette