Re: Improving Build Speed

[Martin Jansa <martin.jansa@gmail.com>]

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On Wed, Nov 20, 2013 at 11:43:13PM +0100, Ulf Samuelsson wrote:
> 2013-11-20 22:29, Richard Purdie skrev:
> Another idea:
> 
> I suspect that there is a lot of unpacking and patching of recipes
> for the target when the native stuff is built.
> Does it make sense to have multiple threads reading the disk, for
> the target recipes during the native build or will we just lose out
> due to seek time?
> 
> Having multiple threads accessing the disk, might force the disk to spend
> most of its time seeking.
> Found an application which measures seek time performance,
> and my WD Black will do 83 seeks per second, and my SAS disk will do 
> twice that.
> The RAID of two SAS disks will provide close to SSD throughput (380 MB/s)
> but seek time is no better than a single SAS disk.
> 
> Since there is "empty time" at the end of the native build, does it make 
> sense
> to minimize unpack/patch of target stuff when we reach that point, and
> then we let loose?

In my benchmarks increasing PARALLEL_MAKE till number of cores was
significantly improving build time, but BB_NUMBER_THREADS had minimal
influence somewhere above 6 or 8 (tested on various systems, even only 4 was
optimum on my older RAID-0 and 2 on single disk).
Of course it was quite different for clean build without sstate
prepopulated and build where most of the stuff was reused from sstate.

see http://wiki.webos-ports.org/wiki/OE_benchmark

> ========================
> 
> Now with 48 MB of RAM, (which I might grow to 96 GB, if someone proves that
> this makes it faster), this might be useful to speed things up.
> 
> Can tmpfs beat the kernel cache system?
> 
> 1.    Typically, I work on less than 10 recipes, and if I continuosly
>          rebuild those, why not create the build directories as links to 
> a tmpfs file system.
>          Maybe a configuration file with a list of recipes to build on 
> tmpfs.
> 
>          During a build from scratch, this is not so useful, but once 
> most stuff is in place, it might,
> 
> 2.     If the downloads directory was shadowed in a tmpfs system
>          then there would be less seek time during the build.
>          The downloads tmpfs should be poplulated at boot time,
>          and rsynced with a real disk in the background when new stuff
>          is downloaded from internet.
> 
> 3.     With 96 GB of RAM, maybe the complete build directory will fit.
>          Would be nice to build everything on tmpfs, and automatically rsync
>          to a real disk when there is nothing else to do...
> 
> 4.     If not tmpfs is used, then It would still be good to have better 
> control
>          over the build directory.
>          It make sense to me to have the metadata on an SSD, but the
>          build directory should be on my RAID cluster for fast rebuilds.
>          I can set this up manually, but it would be better to be able to
>          specify this in a configuration file.
> 

See
http://www.mail-archive.com/yocto@yoctoproject.org/msg14879.html

-- 
Martin 'JaMa' Jansa     jabber: Martin.Jansa@gmail.com

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