Hi Thomas, > -----Original Message----- > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > Sent: Wednesday, June 15, 2016 9:19 AM > To: Pattan, Reshma > Cc: dev at dpdk.org; Ananyev, Konstantin > Subject: Re: [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx > callback lists > > 2016-06-15 05:30, Pattan, Reshma: > > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > > > 2016-06-14 10:38, Reshma Pattan: > > > > Added spinlocks around add/remove logic of Rx and Tx callbacks to > > > > avoid corruption of callback lists in multithreaded context. > > > > > > > > Signed-off-by: Reshma Pattan <reshma.pattan at intel.com> > > > > > > Why cb->next is not locked in burst functions? > > It is safe to do "read access" here and doesn't require any locking as > > rx/tx burst is initiated by only local user(control plane) thread. > > > > > Just protecting add/remove but not its usage seems useless. > > Here locks were required around add/remove to protect "write access" > > because write to callback list is now done from 2 threads > > i.e. one from local user thread(control plane) and another from pdump > > control thread(initiated by remote pdump request). > > So read and write can be done by different threads.
Yes, and this is possible even in current DPDK version (16.04). What is added by Reshma's patch - now it is possible to have concurrent write from 2 different thread to that list. > I think the read access would need locking but we do not want it > in fast path. I don't think it would be needed. As I said - read/write interaction didn't change from what we have right now. But if you have some particular scenario in mind that you believe would cause a race condition - please speak up. Konstantin > Are you sure there is no issue in this design?