GSoC: Add SMT/HT awareness to DragonFlyBSD scheduler

[Mihai Carabas]

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Hello,

On Sun, Jul 8, 2012 at 12:29 PM, Mihai Carabas <mihai.carabas at gmail.com>wrote:

> Hello,
>
> This week I worked on an heuristic that sounds like this: always schedule
> a process to the closest cpu relatively to the cpu it had run before.(e.g.:
> try to run on the cpu that had run before, if it isn't free, try on it's
> sibling on the current level (let's say thread level), if no sibling was
> found, go to the next level (which is the core level), and so on). So, in
> other words, the process would be scheduled to the closest cache it can (it
> couldn't be scheduled on the same core, will loose the level1 cache
> hotness, but it can use the level3 cache hotness). Unfortunately, I
> couldn't find a case to make a difference on my corei3. The reason would be
> that the time quanta of a process is big enough in dragonfly that a process
> that is scheduled is able to use a great part of the L1/L2 cache and on a
> context switch the cache will be invalidated. With the L3 cache shared
> among all cores, there will be no gain. I am waiting for access on a
> multi-socket machine, to test it there.
>

This week I haven't done much coding. I tested the heuristic above on
monster (thanks dillon) and on a dual-socket (thanks ftigeot) amd but the
results weren't meaningful. I start adding debug info to see what happens.
It seems that the processes bumps from one CPU to another when there are
more processes than cpus (the setrunqueue bits is the active mechanism for
scheduling, but there is another one - when a process finishes or blocks,
that CPU tries and pull a process from the bsd4 runqueue, but that process
didn't run before on this CPU). I have discussed the issue with Alex and
Matthew and I am currently working out on a solution.

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Hello,<br><br><div class=3D"gmail_quote">On Sun, Jul 8, 2012 at 12:29 PM, M=
ihai Carabas <span dir=3D"ltr"><<a href=3D"mailto:mihai.carabas at gmail.co=
m" target=3D"_blank">mihai.carabas at gmail.com</a>></span> wrote:<br><bloc=
kquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #cc=
c solid;padding-left:1ex">
Hello,<br><br><div>This week I worked on an heuristic that sounds like this=
: always schedule a process to the closest cpu relatively to the cpu it had=
 run before.(e.g.: try to run on the cpu that had run before, if it isn&#39=
;t free, try on it's sibling on the current level (let's say thread=
 level), if no sibling was found, go to the next level (which is the core l=
evel), and so on). So, in other words, the process would be scheduled to th=
e closest cache it can (it couldn't be scheduled on the same core, will=
 loose the level1 cache hotness, but it can use the level3 cache hotness). =
Unfortunately, I couldn't find a case to make a difference on my corei3=
. The reason would be that the time quanta of a process is big enough in dr=
agonfly that a process that is scheduled is able to use a great part of the=
 L1/L2 cache and on a context switch the cache will be invalidated. With th=
e L3 cache shared among all cores, there will be no gain. I am waiting for =
access on a multi-socket machine, to test it there.</div>
</blockquote><div>=A0</div></div><div>This week I haven't done much cod=
ing. I tested the heuristic above on monster (thanks dillon) and on a dual-=
socket (thanks ftigeot)=A0amd but the results weren't meaningful. I sta=
rt adding debug info to see what happens. It seems that the processes bumps=
 from one CPU to another when there are more processes than cpus (the setru=
nqueue bits is the active mechanism for scheduling, but there is another on=
e - when a process finishes or blocks, that CPU tries and pull a process fr=
om the bsd4 runqueue, but that process didn't run before on this CPU). =
I have discussed the issue with Alex and Matthew and I am currently working=
 out on a solution.</div>

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