netdev - Re: [RFC v3 net-next 13/18] net/sched: Introduce the TBS Qdisc

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Date:   Tue, 24 Apr 2018 10:50:04 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>
cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, vinicius.gomes@...el.com,
        richardcochran@...il.com, intel-wired-lan@...ts.osuosl.org,
        anna-maria@...utronix.de, henrik@...tad.us, john.stultz@...aro.org,
        levi.pearson@...man.com, edumazet@...gle.com, willemb@...gle.com,
        mlichvar@...hat.com
Subject: Re: [RFC v3 net-next 13/18] net/sched: Introduce the TBS Qdisc

On Mon, 23 Apr 2018, Jesus Sanchez-Palencia wrote:
> On 03/21/2018 06:46 AM, Thomas Gleixner wrote:
> > On Tue, 6 Mar 2018, Jesus Sanchez-Palencia wrote:
> >> +struct tbs_sched_data {
> >> +	bool sorting;
> >> +	int clockid;
> >> +	int queue;
> >> +	s32 delta; /* in ns */
> >> +	ktime_t last; /* The txtime of the last skb sent to the netdevice. */
> >> +	struct rb_root head;
> > 
> > Hmm. You are reimplementing timerqueue open coded. Have you checked whether
> > you could reuse the timerqueue implementation?
> > 
> > That requires to add a timerqueue node to struct skbuff
> > 
> > @@ -671,7 +671,8 @@ struct sk_buff {
> >  				unsigned long		dev_scratch;
> >  			};
> >  		};
> > -		struct rb_node	rbnode; /* used in netem & tcp stack */
> > +		struct rb_node		rbnode; /* used in netem & tcp stack */
> > +		struct timerqueue_node	tqnode;
> >  	};
> >  	struct sock		*sk;
> > 
> > Then you can use timerqueue_head in your scheduler data and all the open
> > coded rbtree handling goes away.
> 
> 
> I just noticed that doing the above increases the size of struct sk_buff by 8
> bytes - struct timerqueue_node is 32bytes long while struct rb_node is only
> 24bytes long.
> 
> Given the feedback we got here before against touching struct sk_buff at all for
> non-generic use cases, I will keep the implementation of sch_tbs.c as is, thus
> keeping the open-coded version for now, ok?

The size of sk_buff is 216 and the size of sk_buff_fclones is 440
bytes. The sk_buff and sk_buff_fclones kmem_caches use objects sized 256
and 512 bytes because the kmem_caches are created with SLAB_HWCACHE_ALIGN.

So adding 8 bytes to spare duplicated code will not change the kmem_cache
object size and I really doubt that anyone will notice.

Thanks,

	tglx