On Fri, 2017-03-17 at 07:42 +0000, Reshetova, Elena wrote: > Should we then first measure the actual numbers to understand what we > are talking here about? > I would be glad to do it if you suggest what is the correct way to do > measurements here to actually reflect the real life use cases. How have these patches been tested in real life exactly ? Can you quantify number of added cycles per TCP packet, where I expect we have maybe 20 atomic operations in all layers ... (sk refcnt, skb->users, page refcounts, sk->sk_wmem_alloc, sk->sk_rmem_alloc, qdisc ...) Once we 'protect' all of them, cost will be quite high. This translates to more fossil fuel being burnt. one atomic_inc() used to be a single x86 instruction. Rough estimate of refcount_inc() : 0000000000000140 <refcount_inc>: 140: 55 push %rbp 141: 48 89 e5 mov %rsp,%rbp 144: e8 00 00 00 00 callq refcount_inc_not_zero 149: 84 c0 test %al,%al 14b: 74 02 je 14f <refcount_inc+0xf> 14d: 5d pop %rbp 14e: c3 retq 00000000000000e0 <refcount_inc_not_zero>: e0: 8b 17 mov (%rdi),%edx e2: eb 10 jmp f4 <refcount_inc_not_zero+0x14> e4: 85 c9 test %ecx,%ecx e6: 74 1b je 103 <refcount_inc_not_zero+0x23> e8: 89 d0 mov %edx,%eax ea: f0 0f b1 0f lock cmpxchg %ecx,(%rdi) ee: 39 d0 cmp %edx,%eax f0: 74 0c je fe <refcount_inc_not_zero+0x1e> f2: 89 c2 mov %eax,%edx f4: 85 d2 test %edx,%edx f6: 8d 4a 01 lea 0x1(%rdx),%ecx f9: 75 e9 jne e4 <refcount_inc_not_zero+0x4> fb: 31 c0 xor %eax,%eax fd: c3 retq fe: 83 f9 ff cmp $0xffffffff,%ecx 101: 74 06 je 109 <refcount_inc_not_zero+0x29> 103: b8 01 00 00 00 mov $0x1,%eax 108: c3 retq This is simply bloat for most cases. Again, I believe this infrastructure makes sense for debugging kernels. If some vendors are willing to run fully enabled debug kernels, that is their choice. Probably many devices wont show any difference. Have we forced KASAN being enabled in linux kernel, just because it found ~400 bugs so far ? I believe refcount_t infra is not mature enough to be widely used right now. Maybe in few months when we have more flexibility, like existing debugging facilities (CONFIG_DEBUG_PAGEALLOC, CONFIG_DEBUG_PAGE_REF, LOCKDEP, KMEMLEAK, KASAN, ...)
