linux-kernel - Re: [PATCH] sched: Avoid division by zero

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4A9679EC.1030108@gmail.com>
Date:	Thu, 27 Aug 2009 14:19:56 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Yinghai Lu <yinghai@...nel.org>, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	jes@....com, jens.axboe@...cle.com, tglx@...utronix.de,
	mingo@...e.hu, Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [PATCH] sched: Avoid division by zero - really

Peter Zijlstra a écrit :
> When re-computing the shares for each task group's cpu representation we
> need the ratio of weight on each cpu vs the total weight of the sched
> domain.
> 
> Since load-balancing is loosely (read not) synchronized, the weight of
> individual cpus can change between doing the sum and calculating the
> ratio.
> 
> The previous patch dealt with only one of the race scenarios, this patch
> side steps them all by saving a snapshot of all the individual cpu
> weights, thereby always working on a consistent set.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/sched.c |   50 +++++++++++++++++++++++++++++---------------------
>  1 files changed, 29 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 0e76b17..4591054 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1515,30 +1515,29 @@ static unsigned long cpu_avg_load_per_task(int cpu)
>  
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  
> +struct update_shares_data {
> +	unsigned long rq_weight[NR_CPUS];
> +};
> +
> +static DEFINE_PER_CPU(struct update_shares_data, update_shares_data);

ouch... thats quite large IMHO, up to 4096*8 = 32768 bytes per cpu...

Now we have nice dynamic per cpu allocations, we could use it here,
and use nr_cpus instead of NR_CPUS as the array size ?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/