linux-kernel - Re: [RFC PATCH] request: teach the device more intelligent

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Message-ID: <CAH9JG2UqMD=S3e+BupO+8dfEZQy5eZWO2gMhbTPmmjHJFOimtw@mail.gmail.com>
Date:	Tue, 9 Aug 2011 23:04:41 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>, jaxboe@...ionio.com
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de, jh80.chung@...sung.com
Subject: Re: [RFC PATCH] request: teach the device more intelligent

Cc the correct email address of jens

On Tue, Aug 9, 2011 at 12:47 PM, Kyungmin Park <kmpark@...radead.org> wrote:
> Hi Jens
>
> Now eMMC device requires the upper layer information to improve the data
> performance and reliability.
>
> . Context ID
> Using the context information, it can sort out the data internally and improve the performance.
> The main problem is that it's needed to define "What's the context".
> Actually I expect cfq queue has own unique ID but it doesn't so decide to use the pid instead
>
> . Data Tag
> Using the Data Tag (1-bit information), It writes the data at SLC area when it's hot data. So it can make the chip more reliable.
> First I expect the REQ_META but current ext4 doesn't pass the WRITE_META. only use the READ_META. so it needs to investigate it.
>
> With these characteristics, it's helpful to teach the device. After some consideration. it's needed to pass out these information at request data structure.
>
> Can you give your opinions and does it proper fields at requests?
>
> Thank you,
> Kyungmin Park
> ---
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 1f96ad6..d73bfa7 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -3790,6 +3790,7 @@ new_queue:
>        rq->elevator_private[0] = cic;
>        rq->elevator_private[1] = cfqq;
>        rq->elevator_private[2] = cfq_ref_get_cfqg(cfqq->cfqg);
> +       rq->hint.context = (int) cfqq->pid;
>        spin_unlock_irqrestore(q->queue_lock, flags);
>        return 0;
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 0e67c45..0145c10 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -69,6 +69,14 @@ enum rq_cmd_type_bits {
>        REQ_TYPE_ATA_PC,
>  };
>
> +/*
> + * request hint
> + */
> +struct request_hint {
> +       int context;                    /* Context ID */
> +       int hot:1;                      /* Hot/cold data */
> +};
> +
>  #define BLK_MAX_CDB    16
>
>  /*
> @@ -139,6 +147,7 @@ struct request {
>
>        int ref_count;
>
> +       struct request_hint hint;       /* request hint information */
>        void *special;          /* opaque pointer available for LLD use */
>        char *buffer;           /* kaddr of the current segment if available */
>
> --
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