RE: [PATCH v4 7/7] x86/resctrl: Add debug files when mounted with debug option

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Fri, 21 Apr 2023, Moger, Babu wrote:
> > -----Original Message-----
> > From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> > Sent: Thursday, April 20, 2023 3:59 AM
> > To: Moger, Babu <Babu.Moger@amd.com>
> > Cc: corbet@lwn.net; Reinette Chatre <reinette.chatre@intel.com>;
> > tglx@linutronix.de; mingo@redhat.com; bp@alien8.de; fenghua.yu@intel.com;
> > dave.hansen@linux.intel.com; x86@kernel.org; hpa@zytor.com;
> > paulmck@kernel.org; akpm@linux-foundation.org; quic_neeraju@quicinc.com;
> > rdunlap@infradead.org; damien.lemoal@opensource.wdc.com;
> > songmuchun@bytedance.com; peterz@infradead.org; jpoimboe@kernel.org;
> > pbonzini@redhat.com; chang.seok.bae@intel.com;
> > pawan.kumar.gupta@linux.intel.com; jmattson@google.com;
> > daniel.sneddon@linux.intel.com; Das1, Sandipan <Sandipan.Das@amd.com>;
> > tony.luck@intel.com; james.morse@arm.com; linux-doc@vger.kernel.org;
> > LKML <linux-kernel@vger.kernel.org>; bagasdotme@gmail.com;
> > eranian@google.com; christophe.leroy@csgroup.eu; jarkko@kernel.org;
> > adrian.hunter@intel.com; quic_jiles@quicinc.com; peternewman@google.com
> > Subject: Re: [PATCH v4 7/7] x86/resctrl: Add debug files when mounted with
> > debug option
> > 
> > On Wed, 19 Apr 2023, Moger, Babu wrote:
> > 
> > >
> > >
> > > On 4/19/23 08:20, Ilpo Järvinen wrote:
> > > > On Mon, 17 Apr 2023, Babu Moger wrote:
> > > >
> > > >> Add the debug files to the resctrl hierarchy.
> > > >>
> > > >> Signed-off-by: Babu Moger <babu.moger@amd.com>
> > > >> ---
> > > >>  arch/x86/kernel/cpu/resctrl/internal.h |    1 +
> > > >>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |   54
> > +++++++++++++++++++++++++++++++-
> > > >>  2 files changed, 54 insertions(+), 1 deletion(-)
> > > >>
> > > >> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
> > > >> b/arch/x86/kernel/cpu/resctrl/internal.h
> > > >> index 1eac07ebc31b..855109abb480 100644
> > > >> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> > > >> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> > > >> @@ -288,6 +288,7 @@ struct rdtgroup {
> > > >>  #define RFTYPE_TOP			BIT(4)
> > > >>  #define RFTYPE_RES_CACHE		BIT(5)
> > > >>  #define RFTYPE_RES_MB			BIT(6)
> > > >> +#define RFTYPE_DEBUG			BIT(7)
> > > >>  #define RFTYPE_CTRL_INFO		(RFTYPE_INFO |
> > RFTYPE_CTRL)
> > > >>  #define RFTYPE_MON_INFO			(RFTYPE_INFO |
> > RFTYPE_MON)
> > > >>  #define RFTYPE_TOP_INFO			(RFTYPE_INFO |
> > RFTYPE_TOP)
> > > >> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > >> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > >> index 15ded0dd5b09..1ec4359348c2 100644
> > > >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > >> @@ -1880,6 +1880,7 @@ static struct rftype res_common_files[] = {
> > > >>  		.mode		= 0444,
> > > >>  		.kf_ops		= &rdtgroup_kf_single_ops,
> > > >>  		.seq_show	= rdtgroup_rmid_show,
> > > >> +		.fflags		= RFTYPE_BASE | RFTYPE_DEBUG,
> > > >>  	},
> > > >>  	{
> > > >>  		.name		= "schemata",
> > > >> @@ -1909,6 +1910,7 @@ static struct rftype res_common_files[] = {
> > > >>  		.mode		= 0444,
> > > >>  		.kf_ops		= &rdtgroup_kf_single_ops,
> > > >>  		.seq_show	= rdtgroup_closid_show,
> > > >> +		.fflags		= RFTYPE_CTRL_BASE | RFTYPE_DEBUG,
> > > >>  	},
> > > >>
> > > >>  };
> > > >> @@ -2420,6 +2422,49 @@ static int mkdir_mondata_all(struct
> > kernfs_node *parent_kn,
> > > >>  			     struct rdtgroup *prgrp,
> > > >>  			     struct kernfs_node **mon_data_kn);
> > > >>
> > > >> +static void resctrl_add_debug_files(void) {
> > > >> +	struct rftype *rfts, *rft;
> > > >> +	int len;
> > > >> +
> > > >> +	rfts = res_common_files;
> > > >> +	len = ARRAY_SIZE(res_common_files);
> > > >> +
> > > >> +	lockdep_assert_held(&rdtgroup_mutex);
> > > >> +
> > > >> +	for (rft = rfts; rft < rfts + len; rft++) {
> > > >> +		if (rft->fflags & RFTYPE_DEBUG) {
> > > >> +			rft->fflags &= ~RFTYPE_DEBUG;
> > > >
> > > > I don't fully follow why you need to play with ->fflags like this.
> > > >
> > > > Is it for the ->fflags test in rdtgroup_add_files()? Can't you just
> > > > do some extra masking there for RFTYPE_DEBUG based on resctrl_debug
> > > > which you already keep?
> > >
> > > Actually with this change, I can remove all these tricks here.
> > > I don't have to change the check "if (rft->fflags && ((fflags &
> > > rft->fflags) == rft->fflags)) {"
> > >
> > > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > index 1ec4359348c2..b560c44817bb 100644
> > > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > @@ -1925,6 +1925,9 @@ static int rdtgroup_add_files(struct kernfs_node
> > > *kn, unsigned long fflags)
> > >
> > >         lockdep_assert_held(&rdtgroup_mutex);
> > >
> > > +       if (resctrl_debug)
> > > +               fflags |= RFTYPE_DEBUG;
> > 
> > Yes, looks good.
> > 
> > It matches to the idea I had in my mind but doesn't require putting it 
> > into the if condition itself.
>
> Without if condition?  How?  Let me know.

I was referring to the if condition within the loop, not to doing it
without some conditional (I had an (resctrl_debug ? RFTYPE_DEBUG : 0)
construct in my mind).

To remove if, it would, of course, be possible to use another static 
file-level variable but it doesn't seem justified. I think what you 
proposed is fine for this use and looks clean.

-- 
 i.