From mboxrd@z Thu Jan  1 00:00:00 1970
From: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
Subject: Re: [PATCH v2 1/3] iommu/arm-smmu-v3: put off the execution of TLBI*
	to reduce lock confliction
Date: Wed, 18 Oct 2017 13:58:49 +0100
Message-ID: <20171018125849.GD4077@arm.com>
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To: Zhen Lei <thunder.leizhen-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: Kefeng Wang <wangkefeng.wang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, linux-kernel <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Jinyue Li <lijinyue-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, iommu <iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, Libin <huawei.libin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Hanjun Guo <guohanjun-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, linux-arm-kernel <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
List-Id: iommu@lists.linux-foundation.org

Hi Thunder,

On Tue, Sep 12, 2017 at 09:00:36PM +0800, Zhen Lei wrote:
> Because all TLBI commands should be followed by a SYNC command, to make
> sure that it has been completely finished. So we can just add the TLBI
> commands into the queue, and put off the execution until meet SYNC or
> other commands. To prevent the followed SYNC command waiting for a long
> time because of too many commands have been delayed, restrict the max
> delayed number.
> 
> According to my test, I got the same performance data as I replaced writel
> with writel_relaxed in queue_inc_prod.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> ---
>  drivers/iommu/arm-smmu-v3.c | 42 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 37 insertions(+), 5 deletions(-)

If we want to go down the route of explicit command batching, I'd much
rather do it by implementing the iotlb_range_add callback in the driver,
and have a fixed-length array of batched ranges on the domain. We could
potentially toggle this function pointer based on the compatible string too,
if it shows only to benefit some systems.

Will