On Thu, 12 Nov 2020 09:18:21 +0000 David Laight <david.lai...@aculab.com> wrote:
> From: Steven Rostedt > > Sent: 12 November 2020 00:33 > > > > Inspecting the data structures of the function graph tracer, I found that > > the overrun value is unsigned long, which is 8 bytes on a 64 bit machine, > > and not only that, the depth is an int (4 bytes). The overrun can be simply > > an unsigned int (4 bytes) and pack the ftrace_graph_ret structure better. > > > > The depth is moved up next to the func, as it is used more often with func, > > and improves cache locality. > ... > > } __packed; > > Does this many any/much difference given that the structure is > marked __packed? > > OTOH the __packed will (probably) kill performance on systems > that don't support mis-aligned accesses. > I think you answered your own question ;-) That was why I try to keep 4 byte items together. But the point here was that overrun is hardly ever used (probably could just be a single byte), and there was no reason for it to be a long. -- Steve
