Re: Building Kernel and World with -j

[krad]

I use these options in my src.conf

WITH_FAST_DEPEND=yes
WITH_CCACHE_BUILD=yes

I can often get build times of about 9 min but can got upto about 30 mins
in jenkins  depending on how much has changed. This is on a i5-3570K. It
does have 32GB and ssd l2arc. Those times are for a buildworld, buildkernel
packages for pkgbase. and j is set to 5


On 23 January 2017 at 18:09, Kevin Oberman  wrote:

> On Mon, Jan 23, 2017 at 6:10 AM, Lowell Gilbert <
> freebsd-stable-lo...@be-well.ilk.org> wrote:
>
> > Walter Parker  writes:
> >
> > > For decades there has always been a warning not to do parallel builds
> of
> > > the kernel or the world (Linux kernel builds also suggest not to do
> > this).
> > >
> > > Every once in a while, I see people post about 5 minutes. This only
> way I
> > > can see this happening is by doing a parallel build (-j 16 on a Xeon
> > > Monster box).
> > >
> > > Are parallel builds safe? If not, what are actual risk factors and can
> > they
> > > be mitigated?
> >
> > As a general rule, it's safe. But don't report failures from a
> > parallel build.
> >
> > This is not so much an issue of parallel builds being unsupported
> > as of the logs being harder to read.
>
>
> Use of parallel builds of world and kernel are and have been supported
> since at least 10.0. If a parallel build fails, the first step is usually
> to do a single-job build. If it succeeds, there is a bug in the make
> scripts that should be reported. If the single-job build also fails, a bug
> should be reported with any errors included from the non-parallel build as
> the parallel build makes the error context very difficult or even
> impossible to determine from the log.
>
> Generally, I think the number of jobs should be slightly greater than the
> number of available CPU threads. Back in 10.0 days I ran some tests that
> showed the for 4 and 8 thread systems the improvements for large numbers of
> jobs peaked at about CPU thread count + 2 and significantly larger numbers
> of jobs caused a slight deterioration in performance. This was not true on
> early hyper-threaded CPUs which did not effectively optimize
> hyper-threading and things may have changed in the 6 or 7 years since I
> tested and may be very different for systems with large numbers of threads
> seen in servers today.
> --
> Kevin Oberman, Part time kid herder and retired Network Engineer
> E-mail: rkober...@gmail.com
> PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683
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Re: Building Kernel and World with -j

[Kevin Oberman]

On Mon, Jan 23, 2017 at 6:10 AM, Lowell Gilbert <
freebsd-stable-lo...@be-well.ilk.org> wrote:

> Walter Parker  writes:
>
> > For decades there has always been a warning not to do parallel builds of
> > the kernel or the world (Linux kernel builds also suggest not to do
> this).
> >
> > Every once in a while, I see people post about 5 minutes. This only way I
> > can see this happening is by doing a parallel build (-j 16 on a Xeon
> > Monster box).
> >
> > Are parallel builds safe? If not, what are actual risk factors and can
> they
> > be mitigated?
>
> As a general rule, it's safe. But don't report failures from a
> parallel build.
>
> This is not so much an issue of parallel builds being unsupported
> as of the logs being harder to read.


Use of parallel builds of world and kernel are and have been supported
since at least 10.0. If a parallel build fails, the first step is usually
to do a single-job build. If it succeeds, there is a bug in the make
scripts that should be reported. If the single-job build also fails, a bug
should be reported with any errors included from the non-parallel build as
the parallel build makes the error context very difficult or even
impossible to determine from the log.

Generally, I think the number of jobs should be slightly greater than the
number of available CPU threads. Back in 10.0 days I ran some tests that
showed the for 4 and 8 thread systems the improvements for large numbers of
jobs peaked at about CPU thread count + 2 and significantly larger numbers
of jobs caused a slight deterioration in performance. This was not true on
early hyper-threaded CPUs which did not effectively optimize
hyper-threading and things may have changed in the 6 or 7 years since I
tested and may be very different for systems with large numbers of threads
seen in servers today.
--
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rkober...@gmail.com
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683
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Re: Building Kernel and World with -j

[Lowell Gilbert]

Walter Parker  writes:

> For decades there has always been a warning not to do parallel builds of
> the kernel or the world (Linux kernel builds also suggest not to do this).
>
> Every once in a while, I see people post about 5 minutes. This only way I
> can see this happening is by doing a parallel build (-j 16 on a Xeon
> Monster box).
>
> Are parallel builds safe? If not, what are actual risk factors and can they
> be mitigated?

As a general rule, it's safe. But don't report failures from a
parallel build.

This is not so much an issue of parallel builds being unsupported
as of the logs being harder to read.
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Re: Building Kernel and World with -j

[tech-lists]

On 23/01/2017 06:57, Walter Parker wrote:
> Hi,
> 
> For decades there has always been a warning not to do parallel builds of
> the kernel or the world (Linux kernel builds also suggest not to do this).
> 
> Every once in a while, I see people post about 5 minutes. This only way I
> can see this happening is by doing a parallel build (-j 16 on a Xeon
> Monster box).
> 
> Are parallel builds safe? If not, what are actual risk factors and can they
> be mitigated?

I remember warnings to the effect that while buildworld and buildkernel
was safe, installworld and installkernel were not.

I use -j32 on i7 monster boxes.

-- 
J.
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Re: Building Kernel and World with -j

[Steven Hartland]

On 23/01/2017 07:24, Sergei Akhmatdinov wrote:

On Sun, 22 Jan 2017 22:57:46 -0800
Walter Parker  wrote:

For decades there has always been a warning not to do parallel builds of
the kernel or the world (Linux kernel builds also suggest not to do this).

Every once in a while, I see people post about 5 minutes. This only way I
can see this happening is by doing a parallel build (-j 16 on a Xeon
Monster box).

Are parallel builds safe? If not, what are actual risk factors and can they
be mitigated?

Not only do I use -j, I also use ccache.

Another option is to use WITH_META_MODE=YES, that's where most of the 5-minute
reports come from, I imagine. I haven't used it myself.

My kernel takes 10 minutes with world taking about two hours. I generally just
leave them building overnight.

The risks of parallel builds are mostly in the past, concurrency was still just
coming out and there were chances that something would get compiled before it's
dependency, breaking your compile and wasting all of those hours.

Cheers,

We always use -j for both kernel and world for years.

While there's been a few niggles if the clock is out and its a rebuild 
they have been few and far between.


Current cut down kernel build time is 1m and world build time is 22m 
here for FreeBSD 11.0-RELEASE on a dual E5-2640.


Regards
Steve
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Re: Building Kernel and World with -j

[Sergei Akhmatdinov]

On Sun, 22 Jan 2017 22:57:46 -0800
Walter Parker  wrote:
> For decades there has always been a warning not to do parallel builds of
> the kernel or the world (Linux kernel builds also suggest not to do this).
> 
> Every once in a while, I see people post about 5 minutes. This only way I
> can see this happening is by doing a parallel build (-j 16 on a Xeon
> Monster box).
> 
> Are parallel builds safe? If not, what are actual risk factors and can they
> be mitigated?
Not only do I use -j, I also use ccache.

Another option is to use WITH_META_MODE=YES, that's where most of the 5-minute
reports come from, I imagine. I haven't used it myself.

My kernel takes 10 minutes with world taking about two hours. I generally just
leave them building overnight.

The risks of parallel builds are mostly in the past, concurrency was still just
coming out and there were chances that something would get compiled before it's
dependency, breaking your compile and wasting all of those hours.

Cheers,
-- 
Sergei Akhmatdinov

My GPG public key:
gpg --keyserver pgp.mit.edu --recv-keys AD800D99


pgpGLxb_q_7JW.pgp
Description: OpenPGP digital signature

Building Kernel and World with -j

[Walter Parker]

Hi,

For decades there has always been a warning not to do parallel builds of
the kernel or the world (Linux kernel builds also suggest not to do this).

Every once in a while, I see people post about 5 minutes. This only way I
can see this happening is by doing a parallel build (-j 16 on a Xeon
Monster box).

Are parallel builds safe? If not, what are actual risk factors and can they
be mitigated?


Walter

-- 
The greatest dangers to liberty lurk in insidious encroachment by men of
zeal, well-meaning but without understanding.   -- Justice Louis D. Brandeis
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