On Fri, Nov 02, 2018 at 10:07:02PM +0000, Saeed Mahameed wrote: > On Fri, 2018-11-02 at 14:39 -0700, Eric Dumazet wrote: > > > > On 11/02/2018 02:05 PM, Saeed Mahameed wrote: > > > > > temp will be mem copied to priv->stats.sw at the end, > > > memcpy(&priv->stats.sw, &s, sizeof(s)); > > > > > > one other way to solve this as suggested by Andrew, is to get rid > > > of > > > the temp var and make it point directly to priv->stats.sw > > > > > > > What about concurrency ? > > > > This temp variable is there to make sure concurrent readers of stats > > might > > not see mangle data (because another 'reader' just did a memset() and > > is doing the folding) > > > > > > mlx5e_get_stats() can definitely be run at the same time by multiple > > threads. > > > > hmm, you are right, i was thinking that mlx5e_get_Stats will trigger a > work to update stats and grab the state_lock, but for sw stats this is > not the case it is done in place. That was my guess when I saw this.. the confusing bit is why is there s and temp, why not just s? > BTW memcpy itself is not thread safe. At least on 64 bit memcpy will do > 8 byte stores when copying so on most architectures it will cause individual new or old u64 to be returned and not a mess.. 32 bit will always make a mess. If the stats don't update that often then kmalloc'ing a new buffer and RCU'ing it into view might be a reasonable alternative to this? Jason
