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Date:   Tue, 2 Feb 2021 12:16:33 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Avri Altman <avri.altman@wdc.com>
Cc:     "James E . J . Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Bart Van Assche <bvanassche@acm.org>,
        yongmyung lee <ymhungry.lee@samsung.com>,
        Daejun Park <daejun7.park@samsung.com>,
        alim.akhtar@samsung.com, asutoshd@codeaurora.org,
        Zang Leigang <zangleigang@hisilicon.com>,
        Avi Shchislowski <avi.shchislowski@wdc.com>,
        Bean Huo <beanhuo@micron.com>, cang@codeaurora.org,
        stanley.chu@mediatek.com
Subject: Re: [PATCH v2 3/9] scsi: ufshpb: Add region's reads counter
Message-ID: <YBk0kaymYOrrBr8h@kroah.com>
References: <20210202083007.104050-1-avri.altman@wdc.com>
 <20210202083007.104050-4-avri.altman@wdc.com>
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On Tue, Feb 02, 2021 at 10:30:01AM +0200, Avri Altman wrote:
> In host control mode, reads are the major source of activation trials.
> Keep track of those reads counters, for both active as well inactive
> regions.
> 
> We reset the read counter upon write - we are only interested in "clean"
> reads.  less intuitive however, is that we also reset it upon region's
> deactivation.  Region deactivation is often due to the fact that
> eviction took place: a region become active on the expense of another.
> This is happening when the max-active-regions limit has crossed. If we
> don’t reset the counter, we will trigger a lot of trashing of the HPB
> database, since few reads (or even one) to the region that was
> deactivated, will trigger a re-activation trial.
> 
> Keep those counters normalized, as we are using those reads as a
> comparative score, to make various decisions.
> If during consecutive normalizations an active region has exhaust its
> reads - inactivate it.
> 
> Signed-off-by: Avri Altman <avri.altman@wdc.com>
> ---
>  drivers/scsi/ufs/ufshpb.c | 109 ++++++++++++++++++++++++++++++++------
>  drivers/scsi/ufs/ufshpb.h |   6 +++
>  2 files changed, 100 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshpb.c b/drivers/scsi/ufs/ufshpb.c
> index 61de80a778a7..de4866d42df0 100644
> --- a/drivers/scsi/ufs/ufshpb.c
> +++ b/drivers/scsi/ufs/ufshpb.c
> @@ -16,6 +16,9 @@
>  #include "ufshpb.h"
>  #include "../sd.h"
>  
> +#define WORK_PENDING 0

This should be next to the variable you define that uses this, right?
Otherwise we would think this is a valid value, when in reality it is
the bit number, correct?

> +#define ACTIVATION_THRSHLD 4 /* 4 IOs */

You can spell things out "ACTIVATION_THRESHOLD" :)

thanks,

greg k-h