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@sony.com> 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)