On 7/29/20 3:36 AM, David Laight wrote: > From: Madhavan T. Venkataraman >> Sent: 28 July 2020 19:52 > ... >> trampfd faults are instruction faults that go through a different code path than >> the one that calls handle_mm_fault(). Perhaps, it is the handle_mm_fault() that >> is time consuming. Could you clarify? > Given that the expectation is a few instructions in userspace > (eg to pick up the original arguments for a nested call) > the (probable) thousands of clocks taken by entering the > kernel (especially with page table separation) is a massive > delta. > > If entering the kernel were cheap no one would have added > the DSO functions for getting the time of day. I hear you. BTW, I did not say that the overhead was trivial. I only said that in most cases, applications may not mind that extra overhead. However, since multiple people have raised that as an issue, I will address it. I mentioned before that the kernel can actually supply the code page that sets the context and jumps to a PC and map it so the performance issue can be addressed. I was planning to do that as a future enhancement. If there is a consensus that I must address it immediately, I could do that. I will continue this discussion in my reply to Andy's email. Let us pick it up from there. Thanks. Madhavan > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
