Skip site navigation (1)Skip section navigation (2)
Date:      Wed, 25 Feb 2015 12:21:13 +0200
From:      Konstantin Belousov <kostikbel@gmail.com>
To:        Harrison Grundy <harrison.grundy@astrodoggroup.com>
Cc:        freebsd-arch@freebsd.org
Subject:   Re: locks and kernel randomness...
Message-ID:  <20150225102113.GD74514@kib.kiev.ua>
In-Reply-To: <54EDA128.4000107@astrodoggroup.com>
References:  <20150224231921.GQ46794@funkthat.com> <1424822522.1328.11.camel@freebsd.org> <20150225002956.GT46794@funkthat.com> <2F49527F-2F58-4BD2-B8BE-1B1190CCD4D0@bsdimp.com> <54ED5656.50607@astrodoggroup.com> <20150225090638.GB74514@kib.kiev.ua> <54ED92E5.4010803@astrodoggroup.com> <54ED9A4B.4060802@astrodoggroup.com> <20150225100512.GC74514@kib.kiev.ua> <54EDA128.4000107@astrodoggroup.com>

next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Feb 25, 2015 at 02:17:12AM -0800, Harrison Grundy wrote:
> 
> 
> On 02/25/15 02:05, Konstantin Belousov wrote:
> > On Wed, Feb 25, 2015 at 01:47:55AM -0800, Harrison Grundy wrote:
> >> Three choices here are attached here:
> >> 
> >> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=197922
> >> 
> >> The only remaining one I don't have a patch for is putting a
> >> "real" PRNG in ULE.
> >> 
> >> At this point, as far as ULE goes, It just comes down to picking
> >> from one of those approaches.
> > 
> > The third patch, ' Creates sched_random, using the system used in
> > cpu_search.', seems to miss updating the dpcpu randomval in
> > sched_random(), isn't it ?
> > 
> 
> It does exactly what cpu_search does.
I do not see how it does exactly what cpu_search does.

cpu_search is updating *rndptr:
	rnd = (*rndptr = *rndptr * 69069 + 5) >> 26;

while code in patch is:
+        rndptr = DPCPU_PTR(randomval);
+        rnd = (*rndptr * 69069 + 5) >> 26;

where is the write to *rndptr ?

> 
> I really think the scheduler does not actually need randomness in
> these locations. I've been running for the past few days on a few
> systems here that way for testing purposes without issue.
Why doing the arithmetic then ?

> 
> I'll post a separate call for testers for a patch that overtly removes
> them. ULE has a ton of different methods for balancing load between
> cores (which is why you can turn off the long term balancer entirely).



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20150225102113.GD74514>