> On Sep 10, 2021, at 8:18 AM, Peter Oskolkov <posk@xxxxxxxxxx> wrote: > > On Wed, Sep 8, 2021 at 5:16 PM Prakash Sangappa > <prakash.sangappa@xxxxxxxxxx> wrote: >> >> Including liunx-kernel.. >> >> Resending RFC. This patchset is not final. I am looking for feedback on >> this proposal to share thread specific data for us in latency sensitive >> codepath. > > Hi Prakash, > > I'd like to add here that Jann and I have been discussing a similar > feature for my UMCG patchset: > > https://lore.kernel.org/lkml/CAG48ez0mgCXpXnqAUsa0TcFBPjrid-74Gj=xG8HZqj2n+OPoKw@xxxxxxxxxxxxxx/ Hi Peter, I will take a look. > > In short, due to the need to read/write to the userspace from > non-sleepable contexts in the kernel it seems that we need to have some > form of per task/thread kernel/userspace shared memory that is pinned, > similar to what your sys_task_getshared does. Exactly. For this reason wanted kernel to allocate the pinned memory. Didn’t want to deal with files etc as a large number threads will be using the shared structure mechanism. > > Do you think your sys_task_getshared can be tweaked to return an > arbitrarily-sized block of memory (subject to overall constraints) > rather than a fixed number of "options"? I suppose it could. How big of a size? We don’t want to hold on to arbitrarily large amount of pinned memory. The preference would be for the kernel to decide what is going to be shared based on what functionality/data sharing is supported. In that sense the size is pre defined not something the userspace/application can ask. I have not looked at your use case. > > On a more general note, we have a kernel extension internally at > Google, named "kuchannel", that is similar to what you propose here: > per task/thread shared memory with counters and other stat fields that > the kernel populates and the userspace reads (and some additional > functionality that is not too relevant to the discussion). We have few other use cases for this we are looking at, which I can describe later. -Prakash > > Thanks, > Peter > > [...]
