From: Bernd Petrovitsch > Sent: 19 August 2020 11:22 > > On 19/08/2020 10:16, Muni Sekhar wrote: > > On Tue, Aug 18, 2020 at 11:45 PM peter enderborg > > <peter.enderborg@xxxxxxxx> wrote: > [...] > >> On the 4.4 kernel you dont have > >> > >> +CONFIG_RETPOLINE=y > >> +CONFIG_INTEL_RDT=y > > Thanks! That is helpful. Yes, I see 4.4 kernel don't have the above > > two config options. > > What analysis can be done to narrow down the root cause? > > Any example of reference could be helpful to understand. > > I haven't checked the date of the older kernel but Spectre+ > Meltdown mitigation costs a lot (20%-30% speed IIRC, out > of the top of my head). It depends greatly on the benchmark. Page table separation has a massive effect on anything that does a lot of short system calls. There may be some mitigation in very recent hardware. And I can't remember if it gets disabled for 'root' processes (which can read kernel memory anyway). It is definitely worth building a kernel with the mitigations disabled - if only to check that they are responsible. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
