On Mon, Jun 07, 2021 at 02:37:16PM +0300, Leon Romanovsky wrote: > On Mon, Jun 07, 2021 at 01:22:26PM +0200, Greg KH wrote: > > On Mon, Jun 07, 2021 at 01:51:36PM +0300, Leon Romanovsky wrote: > > > On Mon, Jun 07, 2021 at 12:25:03PM +0200, Greg KH wrote: > > > > On Mon, Jun 07, 2021 at 11:17:35AM +0300, Leon Romanovsky wrote: > > > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > > > > > > > > > This code is trying to attach a list of counters grouped into 4 groups to > > > > > the ib_port sysfs. Instead of creating a bunch of kobjects simply express > > > > > everything naturally as an ib_port_attribute and add a single > > > > > attribute_groups list. > > > > > > > > > > Remove all the naked kobject manipulations. > > > > > > > > Much nicer. > > > > > > > > But why do you need your counters to be atomic in the first place? What > > > > are they counting that requires this? Given that they are just a > > > > statistic for userspace, making them be a u64 should work just the same, > > > > right? > > > > > > The statistic counters are per-port, while the cm.c flows run in > > > asynchronically in parallel for every CM connection. > > > > > > We need atomic variable to ensure that "write to u64" is not > > > interrupted. > > > > On what system is "write to u64" interruptable? > > On 32 bits, and yes, we have a customer who still uses such system. So you will see what, a "tear"? Or a stale value? > > As these are per-port, do multiple threads try to increment these at > > the same time? > > Yes, CM connection can be seen as thread. Bottom line everything in parallel. > > > And even if they do, what happens if one is 'dropped' somehow because of this? > > Probably nothing, we increment the statistics only. So you are hitting cache lines for no good reason, probably not a good idea, you are wasting cpu cycles for nothing :( thanks, greg k-h
