netdev - Re: [RFC] net/core/dst.c : Should'nt dst_run_gc() be more scalable and friendly ?

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Date:	Thu, 16 Aug 2007 15:36:19 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC] net/core/dst.c : Should'nt dst_run_gc() be more scalable
 and friendly ?

On Thu, 16 Aug 2007 20:41:58 +0800
Herbert Xu <herbert@...dor.apana.org.au> wrote:

> Eric Dumazet <dada1@...mosbay.com> wrote:
> >
> > I am wondering how to really solve the problem. Could a workqueue be used here instead of a timer ?
> 
> I think so.
> 
> A mutex would separate the GC and dst_ifdown.  You'd take the
> spin lock in the GC only to replace the garbage list with NULL.
> You then drop the lock to process it.  Once it's done you take
> the lock again and join it with whatever that's been added in
> the mean time.  This is easy because you should already have
> the tail after the GC process.

Thanks Herbert

Yes, I already did this (with the current softirq based timer model),
 but how can dst_dev_event() do its work, since the GC is using 
a private list. (In my patch, time to GC process XXX.000 entries is about XX seconds.)

We would have to change dst_dev_event() to :
- Signal to GC it has to stop as soon as possible.
- Wait for GC be stoped (busy wait I suspect we cannot sleep in dst_dev_event() ? )
, giving us a full garbage_list.
- Process the whole list.
- Restart GC

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