From: Artem Bityutskiy > > Sent: 31 January 2020 11:24 > On Fri, 2020-01-31 at 11:07 +0000, David Laight wrote: > > Unless you know exactly which cpu table is being used the > > only constraint a user can request is the latency. > > Hi David, > > in all my use-cases I always know what is the CPU I am dealing with and > what are the C-states. Simply because in my view they are always CPU- > dependent in terms of what they do and how are they named. > > What you say sounds to me like you would want to disable some C-states > without knowing anything (or much) about the CPU you are dealing with > and the C-state names. > > If so, could you please share examples of such use-cases? Dunno, but clearly you want to disable (say) C3 while leaving C6 enabled. I was trying to find why it was taking 600+us for a RT process to get rescheduled when it had only been sleeping for a few us. I found where it was sleeping, but that didn't help at all. Someone pointed me at a 'random' pdf that referred to /dev/cpu_dma_latency. Setting that to a small value (eg 20) helps no end. But there are no references in the code or man pages to that. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
