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Date: Thu, 03 Aug 2017 22:36:08 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Florian Fainelli <f.fainelli@...il.com> Cc: netdev@...r.kernel.org, davem@...emlot.net, Andrew Lunn <andrew@...n.ch>, Vivien Didelot <vivien.didelot@...oirfairelinux.com>, "David S. Miller" <davem@...emloft.net>, open list <linux-kernel@...r.kernel.org> Subject: Re: [PATCH net-next] net: dsa: User per-cpu 64-bit statistics On Thu, 2017-08-03 at 21:33 -0700, Florian Fainelli wrote: > During testing with a background iperf pushing 1Gbit/sec worth of > traffic and having both ifconfig and ethtool collect statistics, we > could see quite frequent deadlocks. Convert the often accessed DSA slave > network devices statistics to per-cpu 64-bit statistics to remove these > deadlocks and provide fast efficient statistics updates. > This seems to be a bug fix, it would be nice to get a proper tag like : Fixes: f613ed665bb3 ("net: dsa: Add support for 64-bit statistics") Problem here is that if multiple cpus can call dsa_switch_rcv() at the same time, then u64_stats_update_begin() contract is not respected. include/linux/u64_stats_sync.h states : * Usage : * * Stats producer (writer) should use following template granted it already got * an exclusive access to counters (a lock is already taken, or per cpu * data is used [in a non preemptable context]) * * spin_lock_bh(...) or other synchronization to get exclusive access * ... * u64_stats_update_begin(&stats->syncp);
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