On Fri, Sep 10, 2021 at 9:13 AM Prakash Sangappa <prakash.sangappa@xxxxxxxxxx> wrote: > > > > > 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. There could be a sysctl or some other mechanism that limits the amount of memory pinned per mm (or per task). Having "options" hardcoded for such a generally useful feature seems limiting... > > 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 > > > > [...] >
