linux-kernel - Re: [PATCH 0/2] iommu/iova: Make the rcache depot properly flexible

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Message-ID: <80fb865a-eb45-e783-277d-0d2e044c28f5@oracle.com>
Date:   Tue, 15 Aug 2023 11:24:53 +0100
From:   John Garry <john.g.garry@...cle.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org
Cc:     will@...nel.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, zhangzekun11@...wei.com
Subject: Re: [PATCH 0/2] iommu/iova: Make the rcache depot properly flexible

On 14/08/2023 18:53, Robin Murphy wrote:
> Hi all,
> 

Hi Robin,

> Prompted by [1], which reminded me I started this a while ago, I've now
> finished off my own attempt at sorting out the horrid lack of rcache
> scalability. It's become quite clear that given the vast range of system
> sizes and workloads there is no right size for a fixed depot array, so I
> reckon we're better off not having one at all.
> 
> Note that the reclaim threshold and rate are chosen fairly arbitrarily -

This threshold is the number of online CPUs, right?

> it's enough of a challenge to get my 4-core dev board with spinning disk
> and gigabit ethernet to push anything into a depot at all :)
> 

I have to admit that I was hoping to also see a more aggressive reclaim 
strategy, where we also trim the per-CPU rcaches when not in use. 
Leizhen proposed something like this a long time ago.

Thanks,
John

> Thanks,
> Robin.
> 
> [1] https://urldefense.com/v3/__https://lore.kernel.org/linux-iommu/20230811130246.42719-1-zhangzekun11@huawei.com__;!!ACWV5N9M2RV99hQ!Oj-N3yDamuhrlNTcuL5MA2LQRVf1EwFxQU21BMXSFBR1Fb3z4H_on1uiFG0EOoYpNc-FKGeoKvw9wzEV_1TRcr4$
> 
> 
> Robin Murphy (2):
>    iommu/iova: Make the rcache depot scale better
>    iommu/iova: Manage the depot list size
> 
>   drivers/iommu/iova.c | 94 ++++++++++++++++++++++++++++++--------------
>   1 file changed, 65 insertions(+), 29 deletions(-)
>