Messages in this thread | | | Subject | Re: [PATCH] x86/resctrl: Fix memory bandwidth counter width for AMD | From | Reinette Chatre <> | Date | Tue, 2 Jun 2020 10:13:10 -0700 |
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Hi Babu,
On 6/1/2020 4:00 PM, Babu Moger wrote: > Memory bandwidth is calculated reading the monitoring counter > at two intervals and calculating the delta. It is the software’s > responsibility to read the count often enough to avoid having > the count roll over _twice_ between reads. > > The current code hardcodes the bandwidth monitoring counter's width > to 24 bits for AMD. This is due to default base counter width which > is 24. Currently, AMD does not implement the CPUID 0xF.[ECX=1]:EAX > to adjust the counter width. But, the AMD hardware supports much > wider bandwidth counter with the default width of 44 bits. > > Kernel reads these monitoring counters every 1 second and adjusts the > counter value for overflow. With 24 bits and scale value of 64 for AMD, > it can only measure up to 1GB/s without overflowing. For the rates > above 1GB/s this will fail to measure the bandwidth. > > Fix the issue setting the default width to 44 bits by adjusting the > offset. > > AMD future products will implement the CPUID 0xF.[ECX=1]:EAX. > > Signed-off-by: Babu Moger <babu.moger@amd.com>
There is no fixes tag but if I understand correctly this issue has been present since AMD support was added to resctrl. This fix builds on top of a recent feature addition and would thus not work for earlier kernels. Are you planning to create a different fix for earlier kernels?
Reinette
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