Messages in this thread | | | Date | Mon, 19 Nov 2007 14:48:46 -0800 | From | Stephane Eranian <> | Subject | Re: [perfmon] Re: [perfmon2] perfmon2 merge news |
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Paul,
On Tue, Nov 20, 2007 at 08:43:32AM +1100, Paul Mackerras wrote: > David Miller writes: > > > As a result I've found that perfmon2 is quite nice and allows > > incredibly useful and powerful tools to be written. The syscalls > > aren't that bad and really I see not reason to block it's inclusion. > > > > I rescind all of my earlier objections, let's merge this soon :-) > > Strongly agree. However, I think we need to add structure size > arguments to most of the syscalls so we can extend them later. > Yes, that is one way. It works well if you only extend structures at the end. Given that you need to obtain the file descriptor first via a pfm_create_context call, an alternative could be that you pass a version number to that call to identify the version the application is requesting.
> Also, something I've been meaning to mention to Stephane is that the > use of the cast_ulp() macro in perfmon is bogus and won't work on > 32-bit big-endian platforms such as ppc32 and sparc32. On such
I don't like those cast_ulp() macros. They were put there to avoid compiler warnings on some architectures. Clearly with the big-endian issue, we need to find something else. The bitmap*() macros make unsigned long *.
The interface uses fixed size type to ensure ABI compatibility between 32 and 64 bit modes. This way there is no need to marhsall syscall arguments for a 32-bit app running on a 64-bit host.
Looks like we will have to use bytes (u8) instead. This may have some performance impact as well. Several bitmaps are used in the context/interrupt routines. Even with u8, there is still a problem with the bitmap*() macros. Now, only a small subset of the bitmap() macros are used, so it may be okay to duplicate them for u8.
What do you think?
> platforms you can't take a pointer to an array of u64, cast it to > unsigned long * and expect the kernel bitmap operations to work > correctly on it. At the least you also need to XOR the bit numbers > with 32 on those platforms. Another alternative is to define the > bitmaps as arrays of bytes instead, which eliminates all byte ordering > and wordsize problems (but makes it more tricky to use the kernel > bitmap functions directly). >
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