linux-kernel - RE: [PATCH 1/6] block: add support for carrying a stream ID in a bio

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Date:	Wed, 25 Mar 2015 18:36:50 +0000
From:	Ming Lin-SSI <ming.l@....samsung.com>
To:	Matias Bjørling <m@...rling.me>,
	Jens Axboe <axboe@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH 1/6] block: add support for carrying a stream ID in a bio

> -----Original Message-----
> From: Matias Bjørling [mailto:m@...rling.me]
> Sent: Wednesday, March 25, 2015 1:11 AM
> To: Ming Lin-SSI; Jens Axboe; linux-kernel@...r.kernel.org; linux-
> fsdevel@...r.kernel.org
> Subject: Re: [PATCH 1/6] block: add support for carrying a stream ID in a bio
> 
> >> Pushing it higher is not a big deal as far as the implementation
> >> goes, though
> >> 16 bits might be stealing a bit too much space for this. On 32-bit
> >> archs, we have 18 bits currently free that we can abuse. The Samsung
> >> device supports
> >> 16 streams. That's honestly a lot more than I would expect most
> >> devices to support in hardware, 16 is a lot of open erase blocks and write
> append points.
> >> Obviously the open channel effort would make that more feasible,
> though.
> >
> > Can we use 8 bits at least? I'll test performance with 16 streams.
> >
> 
> Ming, can you provide an example of how streams will be managed for
> multiple applications? I can see how it would be efficient for a single
> application, but how will it be managed for multiple applications?

Multiple applications will get different stream-id.
For example,

Application 1:
stream_id = open_stream(NVME_DEVICE_HANDLE,  ....); //maybe stream-id 1
fadvise(fd, stream_id, 0, POSIX_FADV_STREAMID); 
write(fd, buf, count);
close_stream(NVME_DEVICE_HANDLE, stream_id);

Application 2:
stream_id = open_stream(NVME_DEVICE_HANDLE,  ....); //maybe stream-id 2
fadvise(fd, stream_id, 0, POSIX_FADV_STREAMID); 
write(fd, buf, count);
close_stream(NVME_DEVICE_HANDLE, stream_id);

Thanks,
Ming

> 
> -Matias
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