On 2024-03-06 at 21:54:02 +0000, Luck, Tony wrote: >> Figuring out if SNC is enabled is only one part of the problem, the >> other being whether the kernel supports it. As there is no easy >> interface that simply states SNC support in the kernel one can find that >> information by comparing L3 cache sizes from different sources. Cache >> size reported by /sys/devices/system/node/node0/cpu0/cache/index3/size >> will always show the full cache size even if it's split by enabled SNC. >> On the other hand /sys/fs/resctrl/size has information about L3 size, >> that with kernel support is adjusted for enabled SNC. > >Early versions of the kernel SNC patch series added an info/l3_MON/snc_ways >file to provide this information. I was talked out of it then: > >https://lore.kernel.org/all/f0841866-315b-4727-0a6c-ec60d22ca29c@xxxxxxx/ > >But that discussion didn't consider the question you discuss here: "Does this >instance of the kernel support SNC?" > >So you have a clever solution. But it seems like a roundabout way for >an application to discover whether the kernel has configured resctrl for >SNC mode. > >Should the kernel provide an info/ file listing the SNC configuration? I suppose it would be a benefit for other numa aware applications to have an easy access to this kernel support information. > >If so, what should it be named? "snc_ways" as a kernel variable was >later replaced by "snc_nodes_per_l3_cache". Is that a good filename? "snc_nodes_per_l3_cache" seems okay to me. And I understand that the file content would show SNC mode and the presence or absence of this file would tell if kernel supports SNC? > >-Tony -- Kind regards Maciej Wieczór-Retman
