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Message-ID: <91b58253-f682-49f7-914d-8faf1ce181ef@arm.com>
Date: Tue, 20 Feb 2024 16:27:19 +0000
From: James Morse <james.morse@....com>
To: David Hildenbrand <david@...hat.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>,
Reinette Chatre <reinette.chatre@...el.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
Babu Moger <Babu.Moger@....com>, shameerali.kolothum.thodi@...wei.com,
D Scott Phillips OS <scott@...amperecomputing.com>,
carl@...amperecomputing.com, lcherian@...vell.com,
bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
dfustini@...libre.com, amitsinght@...vell.com
Subject: Re: [PATCH v9 09/24] x86/resctrl: Use __set_bit()/__clear_bit()
instead of open coding
Hi David,
On 20/02/2024 16:00, David Hildenbrand wrote:
> On 13.02.24 19:44, James Morse wrote:
>> The resctrl CLOSID allocator uses a single 32bit word to track which
>> CLOSID are free. The setting and clearing of bits is open coded.
>>
>> Convert the existing open coded bit manipulations of closid_free_map
>> to use __set_bit() and friends. These don't need to be atomic as this
>> list is protected by the mutex.
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index dcffd1c4a476..bc6e0f83c847 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
>> * - Our choices on how to configure each resource become progressively more
>> * limited as the number of resources grows.
>> */
>
> That comment talks about "free CLOSIDs in a single integer". Once could think about
> rephrasing that to "free CLOSIDs in a simple bitmap."
>
>> -static int closid_free_map;
>> +static unsigned long closid_free_map;
>> static int closid_free_map_len;
>> int closids_supported(void)
>> @@ -130,8 +130,8 @@ static void closid_init(void)
>> closid_free_map = BIT_MASK(rdt_min_closid) - 1;
>
> Now that we use "unsigned long", I was wondering for a second if we should use "proper"
> bitmap functions here like
>
> bitmap_fill(closid_free_map, rdt_min_closid);
>
> and converting the alloc path (replace ffs() in closid_alloc()):
>
> closid = find_first_bit(closid_free_map, closid_free_map_len);
> if (closid == closid_free_map_len)
> return -ENOSPC;
> __clear_bit(closid, &closid_free_map);
>
> (would get rid of the closid-- in closid_alloc())
Yup. I have this as something to post after all the MPAM changes as it's not necessary to
get MPAM going. The patch[0] uses the bitmap APIs you suggest to remove the fixed limit on
the number of CLOSID/PARTID.
MPAM systems are being built with more than 32, but will work without that patch.
> Just a thought, so
>
> Reviewed-by: David Hildenbrand <david@...hat.com>
Thanks!
James
[0]
https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/commit/?h=mpam/snapshot/v6.7-rc2&id=b530deed244d9b45f3bce3cccde91f6ed0ebf7ea
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