linux-kernel - RE: [PATCH v11 20/31] fs/resctrl: Refactor Sub-NUMA Cluster (SNC) in mkdir/rmdir code flow

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <SJ1PR11MB608328747C28F736C6DD5FCFFCEEA@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Thu, 9 Oct 2025 21:31:16 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>
CC: Fenghua Yu <fenghuay@...dia.com>, "Wieczor-Retman, Maciej"
	<maciej.wieczor-retman@...el.com>, Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>, "Drew
 Fustini" <dfustini@...libre.com>, Dave Martin <Dave.Martin@....com>, "Chen,
 Yu C" <yu.c.chen@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v11 20/31] fs/resctrl: Refactor Sub-NUMA Cluster (SNC) in
 mkdir/rmdir code flow

> > There are only two places where SNC mode is checked in this way. The
> > others rely on seeing that mon_data::sum is set, or that rr->hdr is
> > NULL. So it seems like a very small improvement.
>
> This is not about SNC mode or not but instead about this code being L3
> resource specific.
>
> I see the mon_data::sum and rr->hdr checks as supporting a separate
> feature that was introduced to support SNC - it should not be used as
> a check for SNC support even though it currently implies this due to SNC
> being the only user. Could we not, hypothetically, even use these properties
> in the region aware MBM work?
>
> > If we ever add a node scoped resource that isn't related to SNC, it
> > would be needed at that point. But I'm not sure why hardware would
> > ever do that.
>
> Right. This is not about just what is needed to enable this feature but
> about making the code easy to follow for those that attempt to understand,
> debug, and/or build on top.

Reinette,

Region aware MBM work will need to sum things to support legacy resctrl
"mbm_total_bytes". But while SNC sums across domains that share the
same cache id inside the same resource, we may be summing across
different resources (assuming we go with separate resources per region)
or summing across regions within a domain (if we bundle the regions into a new
struct rdt_region_mon_domain).

So __mon_event_count() will need to get additional refactoring and helper
functions, and struct mon_data an additional field to say that this other
"sum" function must be used.

-Tony