On Mon, Oct 29, 2018 at 7:25 PM, Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote: > This patch introduces a new /proc/stat2 file that is identical to the > regular 'stat' except that it zeroes all hard irq statistics. The new > file is a drop in replacement to stat for users that need performance. For a while now, I've been thinking over ways to improve the performance of collecting various bits of kernel information. I don't think that a proliferation of special-purpose named bag-of-fields file variants is the right answer, because even if you add a few info-file variants, you're still left with a situation where a given file provides a particular caller with too little or too much information. I'd much rather move to a model in which userspace *explicitly* tells the kernel which fields it wants, with the kernel replying with just those particular fields, maybe in their raw binary representations. The ASCII-text bag-of-everything files would remain available for ad-hoc and non-performance critical use, but programs that cared about performance would have an efficient bypass. One concrete approach is to let users open up today's proc files and, instead of read(2)ing a text blob, use an ioctl to retrieve specified and targeted information of the sort that would normally be encoded in the text blob. Because callers would open the same file when using either the text or binary interfaces, little would have to change, and it'd be easy to implement fallbacks when a particular system doesn't support a particular fast-path ioctl.
