06-16-2010
The performance impact is highly workload dependent, but on a fairly typical kernel compile,the PAE penalty works out to be around a 1% performance hit on RedHat’s test boxes.Testing with various other workload mixes has given performance
hits ranging from 0% to 10%.
From Redhat's 2.1 Virtual memory white paper. Things may have changed slightly in 2.6, but as such, it will still produce a slight performance hit.
Last edited by mark54g; 06-16-2010 at 10:52 PM..
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LEARN ABOUT DEBIAN
ibv_fork_init
IBV_FORK_INIT(3) Libibverbs Programmer's Manual IBV_FORK_INIT(3)
NAME
ibv_fork_init - initialize libibverbs to support fork()
SYNOPSIS
#include <infiniband/verbs.h>
int ibv_fork_init(void);
DESCRIPTION
ibv_fork_init() initializes libibverbs's data structures to handle fork() function calls correctly and avoid data corruption, whether
fork() is called explicitly or implicitly (such as in system()).
It is not necessary to use this function if all parent process threads are always blocked until all child processes end or change address
spaces via an exec() operation.
RETURN VALUE
ibv_fork_init() returns 0 on success, or the value of errno on failure (which indicates the failure reason).
NOTES
ibv_fork_init() works on Linux kernels supporting the MADV_DONTFORK flag for madvise() (2.6.17 and higher).
Setting the environment variable RDMAV_FORK_SAFE or IBV_FORK_SAFE has the same effect as calling ibv_fork_init().
Setting the environment variable RDMAV_HUGEPAGES_SAFE tells the library to check the underlying page size used by the kernel for memory
regions. This is required if an application uses huge pages either directly or indirectly via a library such as libhugetlbfs.
Calling ibv_fork_init() will reduce performance due to an extra system call for every memory registration, and the additional memory allo-
cated to track memory regions. The precise performance impact depends on the workload and usually will not be significant.
Setting RDMAV_HUGEPAGES_SAFE adds further overhead to all memory registrations.
SEE ALSO
fork(2), wait(2), system(3), exec(3), ibv_get_device_list(3)
AUTHORS
Dotan Barak <dotanba@gmail.com>
libibverbs 2006-10-31 IBV_FORK_INIT(3)