> On Oct 13, 2021, at 11:59 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Wed, Oct 13, 2021 at 10:46:49AM -0400, Chuck Lever wrote: >> This patch series moves forward with the removal of dprintk in >> SUNRPC in favor of tracepoints. This is the last step for the >> svcrdma component. > > Makes sense to me. > > I would like some (very short) documentation, somewhere. Partly just > for my sake! I'm not sure exactly what to recommend to bug reporters. > > I guess > > trace-cmd record -e 'sunrpc:*' > trace-cmd report > > would be a rough substitute for "rpcdebug -m rpc -s all"? It would, but tracepoints can be enabled one event at a time. If you're looking for a direct replacement for a specific rpcdebug invocation, it might be better to examine the current sunrpc debug facilities and provide specific command lines to mimic those. "rpcdebug -vh" gives us: rpc xprt call debug nfs auth bind sched trans svcsock svcdsp misc cache all nfs vfs dircache lookupcache pagecache proc xdr file root callback client mount fscache pnfs pnfs_ld state all nfsd sock fh export svc proc fileop auth repcache xdr lockd all nlm svc client clntlock svclock monitor clntsubs svcsubs hostcache xdr all If tracepoints are named carefully, we can provide specific command lines to enable them as groups. So, for instance, I was thinking rpcdebug might display: trace-cmd list | grep svcrdma to list tracepoints related to server side RDMA, or: trace-cmd list | grep svcsock to show tracepoints related to server side sockets. Then: trace-cmd record -e sunrpc:svcsock\* enables just the socket-related trace events, which coincidentally happens to line up with: rpcdebug -m rpc -s svcsock > Do we have a couple examples of issues that could be diagnosed with > tracepoints? Anything you can do with dprintk you can do with trace points. Plus because tracepoints are lower overhead, they can be enabled and used in production environments, unlike dprintk. Also, tracepoints can trigger specific user space actions when they fire. You could for example set up a tracepoint in the RPC client that fires when a retransmit timeout occurs, and it could trigger a script to start tcpdump. > In the past I don't feel like I've ended up using dprintks > all that much; somehow they're not usually where I need them. But maybe > that's just me. And maybe as we put more thought into where tracepoints > should be, they'll get more useful. > Documentation/filesystems/nfs/, or the linux-nfs wiki, could be easy > places to put it. Though *something* in the man pages would be nice. > At a minimum, a warning in rpcdebug(8) that we're gradually phasing out > dprintks. As I understood the conversation last week, SteveD and DaveW volunteered to be responsible for changes to rpcdebug? So far we haven't had much documentation for dprintk. That means we are starting more or less from scratch for explaining observability in the NFS stacks. Free rein, and all that. -- Chuck Lever
