Re: [PATCH 1/1] x86/platform/x86: Fix count of CHas on multi-pci-segment arches

[Liang, Kan]

On 3/13/2018 1:06 AM, Kroening, Gary wrote:
> Thanks, Kan -- your patch looks good, and cleaner than the previous method!
>
> Tonight, I've tested it on our in-house simulator for the following configurations. The simulator has been matching hardware well for this issue -- we'll do more testing on real hardware, but I'm confident you have it right.

That's great. Thanks a lot for the verification. :)

Thanks,
Kan

> Terminology:
>
> "hubless" -- equivalent to "glueless" or "white box" where our BIOS sets things up with a single bus for all sockets.
>
> "scalable" -- BIOS assigns a new segment/domain for each socket
>
> Configurations tested so far:
> - single-socket hubless/scalable
> - two sockets, scalable
> - four sockets, hubless
> - eight sockets, scalable
>
> In all cases, skx_count_chabox() is returning 28 for Skylake server.
> Thanks for the quick response!
> Gary
>
> > -----Original Message-----
> > From: Liang, Kan [mailto:kan.liang@xxxxxxxxxxxxxxx]
> > Sent: Monday, March 12, 2018 8:43 PM
> > To: Kroening, Gary; mingo@xxxxxxxxxx; hpa@xxxxxxxxx; tglx@xxxxxxxxxxxxx;
> > peterz@xxxxxxxxxxxxx
> > Cc: Travis, Mike; Banman, Andrew; Sivanich, Dimitri; Anderson, Russ;
> > x86@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH 1/1] x86/platform/x86: Fix count of CHas on multi-pci-
> > segment arches
> >
> >
> >
> > On 3/7/2018 3:33 PM, Kroening, Gary wrote:
> > > For systems with a single PCI segment, it is sufficient to look for the
> > > bus number to change in order to determine that all of the CHa's have
> > > been counted for a single socket.
> > >
> > > However, for multi PCI segment systems, each socket is given a new
> > > segment and the bus number does NOT change.  So looking only for the
> > > bus number to change ends up counting all of the CHa's on all sockets
> > > in the system.  This leads to writing CPU MSRs beyond a valid range and
> > > causes an error in ivbep_uncore_msr_init_box().
> > >
> > > The fix is to check for either the bus number or segment number to
> > change.
> > >
> >
> > Hi Gary,
> >
> > There is a recommended way in uncore document to query the number of
> > CHAs on Skylake server.
> > I have a patch to implement the new way.
> >
> > Could you please take a look at the patch and see if it can fix your
> > issue?
> >
> >
> > Thanks,
> > Kan
> >
> > ------
> >   From 55f54b2fa3021c691c2fd4f5cfc8f441fd104e91 Mon Sep 17 00:00:00 2001
> > From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > Date: Mon, 12 Mar 2018 13:03:40 -0700
> > Subject: [PATCH] perf/x86/intel/uncore: Querying number of CHAs from
> > CAPID6 register
> >
> > The number of CHAs is miscalculated on multi PCI domain systems on
> > Skylake server
> >
> > (From Kroening, Gary:
> >
> > For systems with a single PCI segment, it is sufficient to look for the
> > bus number to change in order to determine that all of the CHa's have
> > been counted for a single socket.
> > However, for multi PCI segment systems, each socket is given a new
> > segment and the bus number does NOT change.  So looking only for the
> > bus number to change ends up counting all of the CHa's on all sockets
> > in the system.  This leads to writing CPU MSRs beyond a valid range and
> > causes an error in ivbep_uncore_msr_init_box().)
> >
> > To determine the number of CHAs, it should read bits 27:0 in the CAPID6
> > register located at Device 30, Function 3, Offset 0x9C. These 28 bits
> > form a bit vector of available LLC slices and the CHAs that manage those
> > slices.
> >
> > Fixes: cd34cd97b7b4 ("perf/x86/intel/uncore: Add Skylake server uncore
> > support")
> > Reported-by: Kroening, Gary <gary.kroening@xxxxxxx>
> > Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > ---
> >    arch/x86/events/intel/uncore_snbep.c | 24 ++++++++++--------------
> >    1 file changed, 10 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/x86/events/intel/uncore_snbep.c
> > b/arch/x86/events/intel/uncore_snbep.c
> > index d4672ed..a42715b 100644
> > --- a/arch/x86/events/intel/uncore_snbep.c
> > +++ b/arch/x86/events/intel/uncore_snbep.c
> > @@ -3575,24 +3575,20 @@ static struct intel_uncore_type
> > *skx_msr_uncores[] = {
> >    	NULL,
> >    };
> >
> > +#define SKX_CAPID6		0x9c
> > +#define SKX_CHA_BIT_WIDTH	28
> > +
> >    static int skx_count_chabox(void)
> >    {
> > -	struct pci_dev *chabox_dev = NULL;
> > -	int bus, count = 0;
> > +	struct pci_dev *dev = NULL;
> > +	u32 val = 0;
> >
> > -	while (1) {
> > -		chabox_dev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x208d,
> > chabox_dev);
> > -		if (!chabox_dev)
> > -			break;
> > -		if (count == 0)
> > -			bus = chabox_dev->bus->number;
> > -		if (bus != chabox_dev->bus->number)
> > -			break;
> > -		count++;
> > -	}
> > +	dev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x2083, dev);
> > +	if (!dev)
> > +		return 0;
> >
> > -	pci_dev_put(chabox_dev);
> > -	return count;
> > +	pci_read_config_dword(dev, SKX_CAPID6, &val);
> > +	return bitmap_weight((unsigned long *)&val, SKX_CHA_BIT_WIDTH);
> >    }
> >
> >    void skx_uncore_cpu_init(void)
> > --
> > 2.7.4