From: John Garry <john.garry@huawei.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, <linux-block@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <linux-scsi@vger.kernel.org>
Subject: Re: [RFC PATCH 0/2] sbitmap: NUMA node spreading
Date: Wed, 11 May 2022 10:57:45 +0100 [thread overview]
Message-ID: <40fd1cc9-15b9-719c-8b8d-118cb156729f@huawei.com> (raw)
In-Reply-To: <YnsaRXzKR5FKjC66@T590>
On 11/05/2022 03:07, Ming Lei wrote:
Hi Ming,
>>> Spreading the memory out does probably make sense, but we need to retain
>>> the fast normal case. Making sbitmap support both, selected at init
>>> time, would be far more likely to be acceptable imho.
>> I wanted to keep the code changes minimal for an initial RFC to test the
>> water.
>>
>> My original approach did not introduce the extra load for normal path and
>> had some init time selection for a normal word map vs numa word map, but the
>> code grew and became somewhat unmanageable. I'll revisit it to see how to
>> improve that.
> I understand this approach just splits shared sbitmap into per-numa-node
> part, but what if all IOs are just from CPUs in one same numa node? Doesn't
> this way cause tag starvation and waste?
>
We would not do this. If we can't find a free bit in one node then we
need to check the others before giving up. This is some of the added
complexity which I hinted at. And things like batch get or RR support
become more complex.
Alternatively we could have the double pointer for numa spreading only,
which would make things simpler. I need to check which is overall
better. Adding the complexity for dealing with numa node sub-arrays may
affect performance also.
Thanks,
John
prev parent reply other threads:[~2022-05-11 9:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 11:14 [RFC PATCH 0/2] sbitmap: NUMA node spreading John Garry
2022-05-10 11:14 ` [RFC PATCH 1/2] sbitmap: Make sbitmap.map a double pointer John Garry
2022-05-10 11:14 ` [RFC PATCH 2/2] sbitmap: Spread sbitmap word allocation over NUMA nodes John Garry
2022-05-10 12:50 ` [RFC PATCH 0/2] sbitmap: NUMA node spreading Jens Axboe
2022-05-10 13:44 ` John Garry
2022-05-10 14:34 ` Jens Axboe
2022-05-10 15:03 ` John Garry
2022-05-11 2:07 ` Ming Lei
2022-05-11 9:57 ` John Garry [this message]
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