linux-kernel - Re: 2.6.24-git4+ regression

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Date:	Thu, 14 Feb 2008 22:25:51 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Lukas Hejtmanek <xhejtman@....muni.cz>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, dhaval@...ux.vnet.ibm.com,
	aneesh.kumar@...ibm.com, efault@....de
Subject: Re: 2.6.24-git4+ regression

On Wed, Jan 30, 2008 at 02:56:09PM +0100, Lukas Hejtmanek wrote:
> Hello,
> 
> I noticed short thread in LKM regarding "sched: add vslice" causes horrible
> interactivity under load.
> 
> I can see similar behavior. If I stress both CPU cores, even typing on
> keyboard suffers from huge latencies, I can see letters appearing with delay
> (typing into xterm). No swap is used at all, having 1GB free RAM.
> 
> I noticed this bad behavior with 2.6.24-git[46], 2.6.24-rc8-git was OK.

Hi Lukas,
	Can you check if the patch below helps improve interactivity for you?

The patch is against 2.6.25-rc1. I would request you to check for
difference it makes with CONFIG_FAIR_GROUP_SCHED and
CONFIG_FAIR_USER_SCHED turned on.

---
 kernel/sched.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

Index: current/kernel/sched.c
===================================================================
--- current.orig/kernel/sched.c
+++ current/kernel/sched.c
@@ -7431,8 +7431,8 @@
 
 			local_load = tg->cfs_rq[i]->load.weight;
 			local_shares = (local_load * total_shares) / total_load;
-			if (!local_shares)
-				local_shares = MIN_GROUP_SHARES;
+			if (!local_load)
+				local_shares = tg->shares;
 			if (local_shares == tg->se[i]->load.weight)
 				continue;
 
@@ -7710,7 +7710,7 @@
 	struct rq *rq = cfs_rq->rq;
 	int on_rq;
 
-	if (!shares)
+	if (shares < MIN_GROUP_SHARES)
 		shares = MIN_GROUP_SHARES;
 
 	on_rq = se->on_rq;

-- 
Regards,
vatsa
--
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