Messages in this thread | | | Date | Sun, 30 Nov 2008 21:38:18 +0200 | From | Török Edwin <> | Subject | Re: [RFC v1][PATCH]page_fault retry with NOPAGE_RETRY |
| |
On 2008-11-28 14:10, Nick Piggin wrote: > This is what I have. > > It does two things. Firstly, it switches x86-64 over to use the xadd > algorithm rather than the spinlock algorithm. This is actually significant > in high contention situations, because the spinlock algorithm doesn't allow > concurrent operations on the lock while the queue of waiters is being > manipulated. > > Secondly, it moves wakeups out from underneath the waiter queue lock. This > is more significant on bigger machines where wakeup latency is worse and/or > runqueue locks are very heavily contended. > > Now both these changes are going to help *mainly* for the case when there are > a significant number of readers and writers, I think. So your write-heavy > workload may not win anything. I noticed some speedup a long time ago on > some weird java (volanomark) workload.
Hi,
I just tested your patch on top of tip/master, and my testprogram has segfaulted :( It is either something wrong in tip/master or the patch, or my program. This is the first time this testprogram segfaults, and it doesn't have a reason to segfault there.
[ 140.624155] scalability[4995]: segfault at 7f9ce137f000 ip 0000000000401a62 sp 00000000454950a0 error 4 in scalability[400000+3000] [ 401.640738] scalability[5398]: segfault at 7fdbffba3000 ip 0000000000401a62 sp 00000000423d70a0 error 4 in scalability[400000+3000]
Here is the relevant portion, at 401a62 I read from the mapping:
static void mmap_worker_fn(int fd, off_t len) { char *data = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0); 401a4f: 48 89 c7 mov %rax,%rdi if(data == MAP_FAILED) { 401a52: 74 36 je 401a8a <mmap_worker_fn+0x5a> perror("mmap"); abort(); 401a54: 31 d2 xor %edx,%edx 401a56: 31 c9 xor %ecx,%ecx static pthread_mutex_t thrtime_mtx = PTHREAD_MUTEX_INITIALIZER;
static size_t execute(const char *data, size_t len) { size_t sum = 0, i; for(i=0;i<len;++i) 401a58: 48 85 db test %rbx,%rbx 401a5b: 74 28 je 401a85 <mmap_worker_fn+0x55> 401a5d: 0f 1f 00 nopl (%rax) if(data[i] == 'd') ++sum; 401a60: 31 c0 xor %eax,%eax 401a62: 80 3c 17 64 cmpb $0x64,(%rdi,%rdx,1) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This simply reads from the mapping
401a66: 0f 94 c0 sete %al static pthread_mutex_t thrtime_mtx = PTHREAD_MUTEX_INITIALIZER;
Steps to reproduce: # sync; echo 3 >/proc/sys/vm/drop_caches; sync # echo 0 >/proc/lock_stat $ sudo ./scalability 16 /usr/bin/ ... prints out results for read, and while running mmap_worker ... ... a message about segmentation fault ....
The testprogram is available here: http://edwintorok.googlepages.com/tst.tar.gz
My .config: http://edwintorok.googlepages.com/config
Can you reproduce the crash on your box? Can I help debugging the problem?
Best regards, --Edwin
| |