Re: why nfs server delay 10ms in nfsd_write()?

[Lee Revell <rlrevell@joe-job.com>]

On Thu, 2005-05-19 at 10:46 +0800, steve wrote:
> i have 2 questions:
> 1.i don't know why do we have to sleep for 10 ms, why not do sync immediately?
> 2.what will happen if we don't sleep for 10ms?
> when i delete these codes, i get a good result, and the write performace improved from 300KB/s to 18MB/s
> 

Did you read the comments in the code?

                /*
                 * Gathered writes: If another process is currently
                 * writing to the file, there's a high chance
                 * this is another nfsd (triggered by a bulk write
                 * from a client's biod). Rather than syncing the
                 * file with each write request, we sleep for 10 msec.
                 *
                 * I don't know if this roughly approximates
                 * C. Juszak's idea of gathered writes, but it's a
                 * nice and simple solution (IMHO), and it seems to
                 * work:-)
                 */
                if (EX_WGATHER(exp)) {
                        if (atomic_read(&inode->i_writecount) > 1
                            || (last_ino == inode->i_ino && last_dev == inode->i_sb->s_dev)) {
                                dprintk("nfsd: write defer %d\n", current->pid);
                                msleep(10);
                                dprintk("nfsd: write resume %d\n", current->pid);
                        }       

                        if (inode->i_state & I_DIRTY) {
                                dprintk("nfsd: write sync %d\n", current->pid);
                                nfsd_sync(file);
                        }       
#if 0
                        wake_up(&inode->i_wait);
#endif
                }


Lee