From: Robin Murphy <robin.murphy@arm.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
frederic@kernel.org, juri.lelli@redhat.com, abelits@marvell.com,
bhelgaas@google.com, linux-pci@vger.kernel.org,
rostedt@goodmis.org, mingo@kernel.org, peterz@infradead.org,
tglx@linutronix.de, davem@davemloft.net,
akpm@linux-foundation.org, sfr@canb.auug.org.au,
stephen@networkplumber.org, rppt@linux.vnet.ibm.com,
jinyuqi@huawei.com, zhangshaokun@hisilicon.com
Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs
Date: Wed, 27 Jan 2021 12:36:30 +0000 [thread overview]
Message-ID: <c5cba5f3-287a-d087-c329-6e6613634370@arm.com> (raw)
In-Reply-To: <20210127121939.GA54725@fuller.cnet>
On 2021-01-27 12:19, Marcelo Tosatti wrote:
> On Wed, Jan 27, 2021 at 11:57:16AM +0000, Robin Murphy wrote:
>> Hi,
>>
>> On 2020-06-25 23:34, Nitesh Narayan Lal wrote:
>>> From: Alex Belits <abelits@marvell.com>
>>>
>>> The current implementation of cpumask_local_spread() does not respect the
>>> isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task,
>>> it will return it to the caller for pinning of its IRQ threads. Having
>>> these unwanted IRQ threads on an isolated CPU adds up to a latency
>>> overhead.
>>>
>>> Restrict the CPUs that are returned for spreading IRQs only to the
>>> available housekeeping CPUs.
>>>
>>> Signed-off-by: Alex Belits <abelits@marvell.com>
>>> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
>>> ---
>>> lib/cpumask.c | 16 +++++++++++-----
>>> 1 file changed, 11 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/lib/cpumask.c b/lib/cpumask.c
>>> index fb22fb266f93..85da6ab4fbb5 100644
>>> --- a/lib/cpumask.c
>>> +++ b/lib/cpumask.c
>>> @@ -6,6 +6,7 @@
>>> #include <linux/export.h>
>>> #include <linux/memblock.h>
>>> #include <linux/numa.h>
>>> +#include <linux/sched/isolation.h>
>>> /**
>>> * cpumask_next - get the next cpu in a cpumask
>>> @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
>>> */
>>> unsigned int cpumask_local_spread(unsigned int i, int node)
>>> {
>>> - int cpu;
>>> + int cpu, hk_flags;
>>> + const struct cpumask *mask;
>>> + hk_flags = HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ;
>>> + mask = housekeeping_cpumask(hk_flags);
>>
>> AFAICS, this generally resolves to something based on cpu_possible_mask
>> rather than cpu_online_mask as before, so could now potentially return an
>> offline CPU. Was that an intentional change?
>
> Robin,
>
> AFAICS online CPUs should be filtered.
Apologies if I'm being thick, but can you explain how? In the case of
isolation being disabled or compiled out, housekeeping_cpumask() is
literally just "return cpu_possible_mask;". If we then iterate over that
with for_each_cpu() and just return the i'th possible CPU (e.g. in the
NUMA_NO_NODE case), what guarantees that CPU is actually online?
Robin.
>> I was just looking at the current code since I had the rare presence of mind
>> to check if something suitable already existed before I start open-coding
>> "any online CPU, but local node preferred" logic for handling IRQ affinity
>> in a driver - cpumask_local_spread() appears to be almost what I want (if a
>> bit more heavyweight), if only it would actually guarantee an online CPU as
>> the kerneldoc claims :(
>>
>> Robin.
>>
>>> /* Wrap: we always want a cpu. */
>>> - i %= num_online_cpus();
>>> + i %= cpumask_weight(mask);
>>> if (node == NUMA_NO_NODE) {
>>> - for_each_cpu(cpu, cpu_online_mask)
>>> + for_each_cpu(cpu, mask) {
>>> if (i-- == 0)
>>> return cpu;
>>> + }
>>> } else {
>>> /* NUMA first. */
>>> - for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
>>> + for_each_cpu_and(cpu, cpumask_of_node(node), mask) {
>>> if (i-- == 0)
>>> return cpu;
>>> + }
>>> - for_each_cpu(cpu, cpu_online_mask) {
>>> + for_each_cpu(cpu, mask) {
>>> /* Skip NUMA nodes, done above. */
>>> if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
>>> continue;
>>>
>
next prev parent reply other threads:[~2021-01-27 12:40 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-25 22:34 [PATCH v4 0/3] Preventing job distribution to isolated CPUs Nitesh Narayan Lal
2020-06-25 22:34 ` [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs Nitesh Narayan Lal
2020-06-29 16:11 ` Nitesh Narayan Lal
2020-07-01 0:32 ` Andrew Morton
2020-07-01 0:47 ` Nitesh Narayan Lal
2021-01-27 11:57 ` Robin Murphy
2021-01-27 12:19 ` Marcelo Tosatti
2021-01-27 12:36 ` Robin Murphy [this message]
2021-01-27 13:09 ` Marcelo Tosatti
2021-01-27 13:49 ` Robin Murphy
2021-01-27 14:16 ` Nitesh Narayan Lal
2021-01-28 15:56 ` Thomas Gleixner
2021-01-28 16:33 ` Marcelo Tosatti
[not found] ` <02ac9d85-7ddd-96da-1252-4663feea7c9f@marvell.com>
2021-02-01 17:50 ` [EXT] " Marcelo Tosatti
2021-01-28 16:02 ` Thomas Gleixner
2021-01-28 16:59 ` Marcelo Tosatti
2021-01-28 17:35 ` Nitesh Narayan Lal
2021-01-28 20:01 ` Thomas Gleixner
[not found] ` <d2a4dc97-a9ed-e0e7-3b9c-c56ae46f6608@redhat.com>
[not found] ` <20210129142356.GB40876@fuller.cnet>
2021-01-29 17:34 ` [EXT] " Alex Belits
[not found] ` <18584612-868c-0f88-5de2-dc93c8638816@redhat.com>
2021-02-05 19:56 ` Thomas Gleixner
2021-02-04 18:15 ` Marcelo Tosatti
2021-02-04 18:47 ` Nitesh Narayan Lal
2021-02-04 19:06 ` Marcelo Tosatti
2021-02-04 19:17 ` Nitesh Narayan Lal
2021-02-05 22:23 ` Thomas Gleixner
2021-02-05 22:26 ` Thomas Gleixner
2021-02-07 0:43 ` Nitesh Narayan Lal
2021-02-11 15:55 ` Nitesh Narayan Lal
2021-03-04 18:15 ` Nitesh Narayan Lal
[not found] ` <faa8d84e-db67-7fbe-891e-f4987f106b20@marvell.com>
2021-03-04 23:23 ` [EXT] " Nitesh Narayan Lal
2021-04-06 17:22 ` Jesse Brandeburg
2021-04-07 15:18 ` Nitesh Narayan Lal
2021-04-08 18:49 ` Nitesh Narayan Lal
2021-04-14 16:11 ` Jesse Brandeburg
2021-04-15 22:11 ` Nitesh Narayan Lal
2021-04-29 21:44 ` Nitesh Lal
2021-04-30 1:48 ` Jesse Brandeburg
2021-04-30 13:10 ` Nitesh Lal
2021-04-30 7:10 ` Thomas Gleixner
2021-04-30 16:14 ` Nitesh Lal
2021-04-30 18:21 ` Thomas Gleixner
2021-04-30 21:07 ` Nitesh Lal
2021-05-01 2:21 ` Jesse Brandeburg
2021-05-03 13:15 ` Nitesh Lal
2020-06-25 22:34 ` [Patch v4 2/3] PCI: Restrict probe functions to housekeeping CPUs Nitesh Narayan Lal
2020-06-25 22:34 ` [Patch v4 3/3] net: Restrict receive packets queuing " Nitesh Narayan Lal
2020-06-26 11:14 ` Peter Zijlstra
2020-06-26 17:20 ` David Miller
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