From: Peter Newman <peternewman@google.com>
To: James Morse <james.morse@arm.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Fenghua Yu <fenghua.yu@intel.com>,
Reinette Chatre <reinette.chatre@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
H Peter Anvin <hpa@zytor.com>, Babu Moger <Babu.Moger@amd.com>,
shameerali.kolothum.thodi@huawei.com,
D Scott Phillips OS <scott@os.amperecomputing.com>,
carl@os.amperecomputing.com, lcherian@marvell.com,
bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com,
xingxin.hx@openanolis.org, baolin.wang@linux.alibaba.com,
Jamie Iles <quic_jiles@quicinc.com>,
Xin Hao <xhao@linux.alibaba.com>,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH v2 09/18] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep
Date: Wed, 22 Mar 2023 14:21:24 +0100 [thread overview]
Message-ID: <CALPaoCjqTtSf1qrvms-==1-ZSEHDDG=Cm2uFeO-DP7JrcKJRkw@mail.gmail.com> (raw)
In-Reply-To: <546a2513-fbfb-da1b-d34b-6c7a2024a861@arm.com>
Hi James,
On Mon, Mar 20, 2023 at 6:12 PM James Morse <james.morse@arm.com> wrote:
> On 10/03/2023 09:28, Peter Newman wrote:
> > In the interest of enabling MPAM functionality, I think the low-effort
> > approach is to only allocate an MBWU monitor to a newly-created MON or
> > CTRL_MON group if one is available. On Intel and AMD, the resources are
> > simply always available.
>
> I agree its low-effort, but I think the result is not worth having.
>
> What does user-space get when it reads 'mbm_total_bytes'? Returning an error here sucks.
> How is user-space supposed to identify the groups it wants to monitor, and those it
> doesn't care about?
>
> Taking "the only way to win is not to play" means the MPAM driver will only offer those
> 'mbm_total_bytes' files if they are going to work in the same way they do today. (as you
> said, on Intel and AMD the resources are simply always available).
I told you that only Intel so far has resources for all RMIDs. AMD
implementations allocate MBW monitors on demand, even reallocating ones
that are actively in use.
> I agree those files have always been able to return errors - but I've never managed to
> make the Intel system I have do it... so I bet user-space doesn't expect errors here.
> (let alone persistent errors)
Find some AMD hardware. It's very easy to get persistent errors due to
no counters being allocated for an RMID:
(this is an 'AMD Ryzen Threadripper PRO 3995WX 64-Cores')
# cd /sys/fs/resctrl/mon_groups
# mkdir test
# cat test/mon_data/*/mbm_total_bytes
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
# cat test/mon_data/*/mbm_total_bytes
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
Unavailable
> This patch to allow resctrl_arch_rmid_read() to sleep is about MPAM's CSU NRDY and the
> high likelyhood that folk build systems where MSCs are sliced up and private to something
> smaller than the resctrl:domain. Without the perf support, this would still be necessary.
I was worried about the blocking more when I thought you were doing it
for MBWU monitoring. Serializing access to limited CSU monitors makes
more sense.
> The changes needed for perf support are to make resctrl_arch_rmid_read() re-entrant, and
> for the domain list to be protected by RCU. Neither of these are as onerous as changes to
> the user-space interface, and the associated risk of breaking programs that work on other
> platforms.
I went ahead and tried to rebase my reliable-MBM-on-AMD changes onto
your series and they seemed to work with less difficulty than I was
expecting, so I'll try to stop worrying about the churn of this series
now.
-Peter
next prev parent reply other threads:[~2023-03-22 13:22 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-13 17:54 [PATCH v2 00/18] x86/resctrl: monitored closid+rmid together, separate arch/fs locking James Morse
2023-01-13 17:54 ` [PATCH v2 01/18] x86/resctrl: Track the closid with the rmid James Morse
2023-01-13 17:54 ` [PATCH v2 02/18] x86/resctrl: Access per-rmid structures by index James Morse
2023-01-17 18:28 ` Yu, Fenghua
2023-03-03 18:33 ` James Morse
2023-01-17 18:29 ` Yu, Fenghua
2023-02-02 23:44 ` Reinette Chatre
2023-03-03 18:33 ` James Morse
2023-01-13 17:54 ` [PATCH v2 03/18] x86/resctrl: Create helper for RMID allocation and mondata dir creation James Morse
2023-01-13 17:54 ` [PATCH v2 04/18] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare() James Morse
2023-01-17 18:28 ` Yu, Fenghua
2023-02-02 23:45 ` Reinette Chatre
2023-03-03 18:33 ` James Morse
2023-01-13 17:54 ` [PATCH v2 05/18] x86/resctrl: Allow RMID allocation to be scoped by CLOSID James Morse
2023-01-17 18:53 ` Yu, Fenghua
2023-03-03 18:34 ` James Morse
2023-02-02 23:45 ` Reinette Chatre
2023-03-03 18:34 ` James Morse
2023-03-10 19:57 ` Reinette Chatre
2023-01-13 17:54 ` [PATCH v2 06/18] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID James Morse
2023-01-17 18:29 ` Yu, Fenghua
2023-03-03 18:35 ` James Morse
2023-02-02 23:46 ` Reinette Chatre
2023-03-03 18:36 ` James Morse
2023-03-10 19:59 ` Reinette Chatre
2023-03-20 17:12 ` James Morse
2023-01-13 17:54 ` [PATCH v2 07/18] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers James Morse
2023-01-17 19:10 ` Yu, Fenghua
2023-03-03 18:37 ` James Morse
2023-02-02 23:47 ` Reinette Chatre
2023-03-06 11:32 ` James Morse
2023-03-08 10:30 ` Peter Newman
2023-03-10 20:00 ` Reinette Chatre
2023-01-13 17:54 ` [PATCH v2 08/18] x86/resctrl: Queue mon_event_read() instead of sending an IPI James Morse
2023-01-17 18:29 ` Yu, Fenghua
2023-03-06 11:32 ` James Morse
2023-03-10 20:00 ` Reinette Chatre
2023-02-02 23:47 ` Reinette Chatre
2023-03-06 11:33 ` James Morse
2023-03-08 16:09 ` James Morse
2023-03-10 20:06 ` Reinette Chatre
2023-03-20 17:12 ` James Morse
2023-01-13 17:54 ` [PATCH v2 09/18] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep James Morse
2023-01-23 13:54 ` Peter Newman
2023-03-06 11:33 ` James Morse
2023-01-23 15:33 ` Peter Newman
2023-03-06 11:33 ` James Morse
2023-03-06 13:14 ` Peter Newman
2023-03-08 17:45 ` James Morse
2023-03-09 13:41 ` Peter Newman
2023-03-09 17:35 ` James Morse
2023-03-10 9:28 ` Peter Newman
2023-03-20 17:12 ` James Morse
2023-03-22 13:21 ` Peter Newman [this message]
2023-01-13 17:54 ` [PATCH v2 10/18] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read() James Morse
2023-01-13 17:54 ` [PATCH v2 11/18] x86/resctrl: Make resctrl_mounted checks explicit James Morse
2023-01-13 17:54 ` [PATCH v2 12/18] x86/resctrl: Move alloc/mon static keys into helpers James Morse
2023-01-13 17:54 ` [PATCH v2 13/18] x86/resctrl: Make rdt_enable_key the arch's decision to switch James Morse
2023-02-02 23:48 ` Reinette Chatre
2023-01-13 17:54 ` [PATCH v2 14/18] x86/resctrl: Add helpers for system wide mon/alloc capable James Morse
2023-01-25 7:16 ` Shaopeng Tan (Fujitsu)
2023-03-06 11:34 ` James Morse
2023-01-13 17:54 ` [PATCH v2 15/18] x86/resctrl: Add cpu online callback for resctrl work James Morse
2023-01-13 17:54 ` [PATCH v2 16/18] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu James Morse
2023-02-02 23:49 ` Reinette Chatre
2023-03-06 11:34 ` James Morse
2023-01-13 17:54 ` [PATCH v2 17/18] x86/resctrl: Add cpu offline callback for resctrl work James Morse
2023-01-13 17:54 ` [PATCH v2 18/18] x86/resctrl: Separate arch and fs resctrl locks James Morse
2023-02-02 23:50 ` Reinette Chatre
2023-03-06 11:34 ` James Morse
2023-03-11 0:22 ` Reinette Chatre
2023-03-20 17:12 ` James Morse
2023-01-25 7:19 ` [PATCH v2 00/18] x86/resctrl: monitored closid+rmid together, separate arch/fs locking Shaopeng Tan (Fujitsu)
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