linux-kernel - Re: [PATCH] scsi: ufs: add missing host_lock in setup_xfer

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Date:   Wed, 14 Jul 2021 11:09:20 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Bean Huo <huobean@...il.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Cc:     Stanley Chu <stanley.chu@...iatek.com>,
        Can Guo <cang@...eaurora.org>, Bean Huo <beanhuo@...ron.com>,
        Asutosh Das <asutoshd@...eaurora.org>
Subject: Re: [PATCH] scsi: ufs: add missing host_lock in setup_xfer_req

On 7/13/21 12:45 PM, Bean Huo wrote:
> This change only impacts on the Samsung exynos platform. and Can's
> optimization patch is to optimise the host_lock,, and removed
> host_lock, now add back in this function makes sense to me.
> but I am thinking how about hba->host_sem?

Hi Bean,

Calls of exynos_ufs_specify_nexus_t_xfer_req() must be serialized, hence 
Jaegeuks' patch. This function is called from the I/O submission path so 
performance matters. My understanding is that spinlocks have less 
overhead than semaphores. Hence the choice for a spinlock.

Thanks,

Bart.