From: James Morse <james.morse@arm.com>
To: Reinette Chatre <reinette.chatre@intel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@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>,
peternewman@google.com
Subject: Re: [PATCH v3 12/19] x86/resctrl: Make resctrl_mounted checks explicit
Date: Thu, 25 May 2023 18:31:56 +0100 [thread overview]
Message-ID: <50775fa5-2da5-90fa-5f6c-9a12b8364e9b@arm.com> (raw)
In-Reply-To: <4b6bd7b9-4701-6344-9a3c-6c7ef25ec6b7@intel.com>
Hi Reinette,
On 28/04/2023 00:37, Reinette Chatre wrote:
> On 4/27/2023 7:19 AM, James Morse wrote:
>> On 01/04/2023 00:28, Reinette Chatre wrote:
>>> On 3/20/2023 10:26 AM, James Morse wrote:
>>>> The rdt_enable_key is switched when resctrl is mounted, and used to
>>>> prevent a second mount of the filesystem. It also enables the
>>>> architecture's context switch code.
>>>>
>>>> This requires another architecture to have the same set of static-keys,
>>>> as resctrl depends on them too.
>>>>
>>>> Make the resctrl_mounted checks explicit: resctrl can keep track of
>>>> whether it has been mounted once. This doesn't need to be combined with
>>>> whether the arch code is context switching the CLOSID.
>>>> Tests against the rdt_mon_enable_key become a test that resctrl is
>>>> mounted and that monitoring is enabled.
>>>
>>> The last sentence above makes the code change hard to follow ...
>>> (see below)
>>>
>>>> This will allow the static-key changing to be moved behind resctrl_arch_
>>>> calls.
>>
>>>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>>>> index f38cd2f12285..6279f5c98b39 100644
>>>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>>>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>>>> @@ -834,7 +834,7 @@ void mbm_handle_overflow(struct work_struct *work)
>>>>
>>>> mutex_lock(&rdtgroup_mutex);
>>>>
>>>> - if (!static_branch_likely(&rdt_mon_enable_key))
>>>> + if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
>>>
>>> ... considering the text in the changelog the "resctrl_mounted" check seems
>>> unnecessary. Looking ahead I wonder if this check would not be more
>>> appropriate in patch 15?
>>
>> How so?
>>
>> This is secretly relying on rdt_mon_enable_key being cleared in rdt_kill_sb() when the
>> filesystem is unmounted, otherwise the overflow thread keeps running once the filesystem
>> is unmounted.
>
> hmmm ... I do not think my feedback was clear. I understand that this is done
> as a prep patch but that was only clear when I read patch 15 because as the
> work is presented here it seems unnecessary.
>
>>
>> I thought it simpler to add all these checks explicitly in one go.
>> That makes it simpler to thin out the static keys as their 'and its mounted' behaviour is
>> no longer relied on.
>
> Understood. If you want to keep this as a prep patch, could you please update the
> changelog to reflect this? The following sentence in the changelog makes this patch
> hard to follow since it essentially claims that what this patch does is unnecessary:
> "Tests against the rdt_mon_enable_key become a test that resctrl is mounted
> and that monitoring is enabled."
"Because of the implicit mount test" ... the text immediately before this.
We're probably going to keep talking past each other on this - I'll rephrase that
paragraph as:
| rdt_mon_enable_key is never used just to test that resctrl is mounted,
| but does also have this implication. Add a resctrl_mounted to all uses
| of rdt_mon_enable_key. This will allow rdt_mon_enable_key to be swapped
| with a helper in a subsequent patch.
> I also do still wonder why these resctrl_mounted checks cannot move to patch
> 15 when they are needed. Adding them there makes it obvious that rdt_mon_enable_key
> had a dual purpose that patch 15 splits into two separate checks.
That is happening in this patch too, rdt_mon_enable_key becomes
(resctrl_mounted && rdt_mon_enable_key), the implicit property is now explicit, so a later
patch can modify rdt_mon_enable_key without breaking this behaviour.
I think its easier to review if patch 15 is making a set of 1:1 mappings instead of
splitting some static-keys but not others. Let me know what you think of the new version.
Thanks,
James
next prev parent reply other threads:[~2023-05-25 17:32 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-20 17:26 [PATCH v3 00/19] x86/resctrl: monitored closid+rmid together, separate arch/fs locking James Morse
2023-03-20 17:26 ` [PATCH v3 01/19] x86/resctrl: Track the closid with the rmid James Morse
2023-03-20 17:26 ` [PATCH v3 02/19] x86/resctrl: Access per-rmid structures by index James Morse
2023-03-21 10:57 ` Ilpo Järvinen
2023-03-31 23:19 ` Reinette Chatre
2023-04-24 13:06 ` Peter Newman
2023-05-25 17:32 ` James Morse
2023-03-20 17:26 ` [PATCH v3 03/19] x86/resctrl: Create helper for RMID allocation and mondata dir creation James Morse
2023-03-21 11:05 ` Ilpo Järvinen
2023-03-31 23:20 ` Reinette Chatre
2023-03-20 17:26 ` [PATCH v3 04/19] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare() James Morse
2023-03-20 17:26 ` [PATCH v3 05/19] x86/resctrl: Allow RMID allocation to be scoped by CLOSID James Morse
2023-03-21 11:29 ` Ilpo Järvinen
2023-03-20 17:26 ` [PATCH v3 06/19] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID James Morse
2023-03-31 23:21 ` Reinette Chatre
2023-04-27 14:09 ` James Morse
2023-03-20 17:26 ` [PATCH v3 07/19] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers James Morse
2023-03-20 17:26 ` [PATCH v3 08/19] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow James Morse
2023-03-21 13:21 ` Ilpo Järvinen
2023-04-27 14:09 ` James Morse
2023-03-21 15:14 ` Ilpo Järvinen
2023-04-27 14:09 ` James Morse
2023-04-27 14:25 ` Ilpo Järvinen
2023-05-25 17:32 ` James Morse
2023-03-31 23:24 ` Reinette Chatre
2023-04-27 14:10 ` James Morse
2023-04-27 23:36 ` Reinette Chatre
2023-05-25 17:32 ` James Morse
2023-03-20 17:26 ` [PATCH v3 09/19] x86/resctrl: Queue mon_event_read() instead of sending an IPI James Morse
2023-03-22 14:07 ` Peter Newman
2023-03-23 9:09 ` Peter Newman
2023-04-27 14:12 ` James Morse
2023-04-27 14:11 ` James Morse
2023-03-31 23:25 ` Reinette Chatre
2023-04-27 14:12 ` James Morse
2023-03-20 17:26 ` [PATCH v3 10/19] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep James Morse
2023-03-31 23:26 ` Reinette Chatre
2023-04-27 14:12 ` James Morse
2023-03-20 17:26 ` [PATCH v3 11/19] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read() James Morse
2023-03-31 23:27 ` Reinette Chatre
2023-04-27 14:19 ` James Morse
2023-04-27 23:40 ` Reinette Chatre
2023-05-25 17:31 ` James Morse
2023-03-20 17:26 ` [PATCH v3 12/19] x86/resctrl: Make resctrl_mounted checks explicit James Morse
2023-03-31 23:28 ` Reinette Chatre
2023-04-27 14:19 ` James Morse
2023-04-27 23:37 ` Reinette Chatre
2023-05-25 17:31 ` James Morse [this message]
2023-03-20 17:26 ` [PATCH v3 13/19] x86/resctrl: Move alloc/mon static keys into helpers James Morse
2023-03-20 17:26 ` [PATCH v3 14/19] x86/resctrl: Make rdt_enable_key the arch's decision to switch James Morse
2023-03-20 17:26 ` [PATCH v3 15/19] x86/resctrl: Add helpers for system wide mon/alloc capable James Morse
2023-03-31 23:29 ` Reinette Chatre
2023-04-27 14:19 ` James Morse
2023-03-20 17:26 ` [PATCH v3 16/19] x86/resctrl: Add cpu online callback for resctrl work James Morse
2023-03-31 23:29 ` Reinette Chatre
2023-03-20 17:26 ` [PATCH v3 17/19] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu James Morse
2023-03-21 15:12 ` Ilpo Järvinen
2023-03-21 15:25 ` Ilpo Järvinen
2023-04-27 14:20 ` James Morse
2023-03-20 17:26 ` [PATCH v3 18/19] x86/resctrl: Add cpu offline callback for resctrl work James Morse
2023-03-21 15:32 ` Ilpo Järvinen
2023-04-27 14:20 ` James Morse
2023-04-27 14:51 ` Ilpo Järvinen
2023-04-05 23:48 ` Reinette Chatre
2023-04-27 14:20 ` James Morse
2023-03-20 17:26 ` [PATCH v3 19/19] x86/resctrl: Separate arch and fs resctrl locks James Morse
2023-05-23 17:14 ` [PATCH v3 00/19] x86/resctrl: monitored closid+rmid together, separate arch/fs locking Tony Luck
2023-05-25 17:31 ` James Morse
2023-05-25 21:00 ` Tony Luck
2023-05-28 20:52 ` Drew Fustini
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