Messages in this thread | | | Date | Mon, 24 Oct 2022 15:37:18 +0800 | From | Feng Tang <> | Subject | Re: [PATCH v1 1/2] x86/tsc: use logical_package as a better estimation of socket numbers |
| |
On Fri, Oct 21, 2022 at 09:21:02AM -0700, Dave Hansen wrote: > On 10/21/22 08:00, Zhang Rui wrote: > > I checked the history of '__max_logical_packages', and realized that > > > > 1. for topology_max_packages()/'__max_logical_packages', the divisor > > 'ncpus' uses cpu_data(0).booted_cores, which is based on the > > *online* CPUs. So when using kernel cmdlines like maxcpus=/nr_cpus=, > > '__max_logical_packages' can get over-estimated. > > > > 2. for 'logical_packages', it equals the number of different physical > > Package IDs for all *online* CPUs. So with kernel cmdlines like > > nr_cpus=/maxcpus=, it can gets under-estimated.
Thanks for raising this new case! For 'maxcpus=' cmdline parameter, I run this on 4-Sockets and 2-Sockets platform, and found the 'logical_packages' is still correct if the 'maxcpus >= (total_cpus/2 + 1)', but gets wrong for smaller numbers.
SRAT parsing solution [1]. can solve 'maxcpus' case, but it will fail for other user cases like sub-numa cluster or 'numa=off' case
IIUC, 'maxcpus' are likely for debug purpose, I think 'logical_packages' is the better option for socket number estimation in the several existing solutions.
> For instance, I can live with the implementation being a bit goofy when > kernel commandlines are in play. We can pr_info() about those cases.
Something like adding
pr_info("Watchdog for TSC is disabled for this platform while estimating the socket number is %d, if the real socket number is bigger than 4 (may due to some tricks like 'maxcpus=' cmdline parameter, please add 'tsc=watchdog' to cmdline as well\n", logical_packages);
and adding a new 'tsc=watchdog' option to force watchdog on (might be over-complexed?)
[1]. https://lore.kernel.org/lkml/Y0UgeUIJSFNR4mQB@feng-clx/
Thanks, Feng
| |