Em Thu, Mar 25, 2021 at 12:55:50AM +0000, Song Liu escreveu:
> > On Mar 23, 2021, at 9:21 AM, Namhyung Kim <namhy...@kernel.org> wrote:
> > #ifdef CONFIG_SECURITY
> > @@ -780,6 +792,14 @@ struct perf_event {
> > #endif /* CONFIG_PERF_EVENTS */
> > };
> > +struct perf_cgroup_node {
> > + struct hlist_node node;
> > + u64 id;
> > + u64 count;
> > + u64 time_enabled;
> > + u64 time_running;
> > + u64 padding[2];
>
> Do we really need the padding? For cache line alignment?
I guess so, to get it to 64 bytes, then having it as:
struct perf_cgroup_node {
struct hlist_node node;
u64 id;
u64 count;
u64 time_enabled;
u64 time_running;
} ____cacheline_aligned;
Seems better :-)
Testing:
[acme@five c]$ cat cacheline_aligned.c
#ifndef ____cacheline_aligned
#define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
#endif
// from ../build/v5.12.0-rc4+/include/generated/autoconf.h
#define CONFIG_X86_L1_CACHE_SHIFT 6
#define L1_CACHE_SHIFT (CONFIG_X86_L1_CACHE_SHIFT)
#define L1_CACHE_BYTES (1 << L1_CACHE_SHIFT)
#ifndef SMP_CACHE_BYTES
#define SMP_CACHE_BYTES L1_CACHE_BYTES
#endif
typedef long long unsigned int u64;
struct hlist_node {
struct hlist_node * next; /* 0 8 */
struct hlist_node * * pprev; /* 8 8 */
/* size: 16, cachelines: 1, members: 2 */
/* last cacheline: 16 bytes */
};
struct perf_cgroup_node {
struct hlist_node node;
u64 id;
u64 count;
u64 time_enabled;
u64 time_running;
} ____cacheline_aligned foo;
[acme@five c]$ cc -g -c -o cacheline_aligned.o cacheline_aligned.c
[acme@five c]$ pahole cacheline_aligned.o
struct hlist_node {
struct hlist_node * next; /* 0 8 */
struct hlist_node * * pprev; /* 8 8 */
/* size: 16, cachelines: 1, members: 2 */
/* last cacheline: 16 bytes */
};
struct perf_cgroup_node {
struct hlist_node node; /* 0 16 */
u64 id; /* 16 8 */
u64 count; /* 24 8 */
u64 time_enabled; /* 32 8 */
u64 time_running; /* 40 8 */
/* size: 64, cachelines: 1, members: 5 */
/* padding: 16 */
} __attribute__((__aligned__(64)));
[acme@five c]$
- Arnaldo
