linux-kernel - Re: [RFC PATCH v2] Add new elevator ops for request hint

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Date:	Thu, 11 Aug 2011 09:14:43 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Kyungmin Park <kmpark@...radead.org>
Cc:	jaxboe@...ionio.com, linux-kernel@...r.kernel.org, arnd@...db.de,
	jh80.chung@...sung.com, linux-mmc@...r.kernel.org
Subject: Re: [RFC PATCH v2] Add new elevator ops for request hint

2011/8/11 Shaohua Li <shli@...nel.org>:
> 2011/8/11 Kyungmin Park <kmpark@...radead.org>:
>> 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.
>>
>> Sample usage is following in drivers/mmc/card/block.c
>>
>>        struct elevator_queue *e = md->queue.queue->elevator;
>>        struct request_hint hint;
>>        int ret;
>>
>>        if (e->ops->elevator_get_req_hint_fn && req)
>>                ret = e->ops->elevator_get_req_hint_fn(req, &hint);
> please put this to blkdev.h or similar. directly using it here
> is abnormal.
BTW, we can add a (rq->cmd_flags & REQ_ELVPRIV) check here to make
sure the request is at io scheduler.
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