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Date: Mon, 23 Jul 2012 11:25:53 -0400 From: Kevin Groeneveld <kgroeneveld@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: netdev@...r.kernel.org Subject: Re: [PATCH] ppp: add 64 bit stats Hi Eric, On Mon, Jul 23, 2012 at 1:16 AM, Eric Dumazet <eric.dumazet@...il.com> wrote: > Hmm. This patches adds races, but also adds a good amount of memory on > these servers with thousand of ppp devices, and 64 cpus. I am curious if you can elaborate on what is racy about the patch, I am still trying to learn. I assumed (possibly incorrectly) that because I was using percpu variables that the stats updates didn't need any extra synchronization as any concurrent updates would be on different cpus. > I really doubt ppp is performance sensitive, it so doesnt need percpu > counter. > > If you really want 64bits stats on ppp, use proper synchronization > around u64 counters (but shared ones) I will work on an updated patch without the percpu variables. I didn't really think about servers with many cpus and many ppp sessions when I created the patch, I was mainly thinking about my Linksys router and other simple clients. Many of the other network drivers use percpu variables for their stats so I just followed along. Would proper synchronization in this case just be wrapping the updates in a spin_lock/spin_unlock? Kevin -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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