- disable nfsd raparms: the new logic do not rely on it
- disable look-ahead on start of file: leave it to the client
For the case of NFS service, the new read-ahead logic
+ can handle disordered nfsd requests
+ can handle concurrent sequential requests on large files
with the help of look-ahead
- will have much ado about the concurrent ones on small files
------------------------------------------------------------------------
Notes about the concurrent nfsd requests issue:
nfsd read requests can be out of order, concurrent and with no ra-state info.
They are handled by the context based read-ahead method, which does the job
in the following steps:
1. scan in page cache
2. make read-ahead decisions
3. alloc new pages
4. insert new pages to page cache
A single read-ahead chunk in the client side will be dissembled and serviced
by many concurrent nfsd in the server side. It is highly possible for two or
more of these parallel nfsd instances to be in step 1/2/3 at the same time.
Without knowing others working on the same file region, they will issue
overlaped read-ahead requests, which lead to many conflicts at step 4.
There's no much luck to eliminate the concurrent problem in general and
efficient ways. But for small to medium NFS servers where the bottleneck
lies in storage devices, here is a performance tip:
# for pid in `pidof nfsd`; do taskset -p 1 $pid; done
This command effectively serializes all nfsd requests. It would be nice if
someone can code this serialization on a per-file basis.
------------------------------------------------------------------------
Here is some test output(8 nfsd; local mount with tcp,rsize=8192):
SERIALIZED, SMALL FILES
=======================
readahead_ratio = 0, ra_max = 128kb (old logic, the ra_max is really not relavant)
96.51s real 11.32s system 3.27s user 160334+2829 cs diff -r $NFSDIR $NFSDIR2
readahead_ratio = 70, ra_max = 1024kb (new read-ahead logic)
94.88s real 11.53s system 3.20s user 152415+3777 cs diff -r $NFSDIR $NFSDIR2
PARALLEL, SMALL FILES
=====================
readahead_ratio = 0, ra_max = 128kb
99.87s real 11.41s system 3.15s user 173945+9163 cs diff -r $NFSDIR $NFSDIR2
readahead_ratio = 70, ra_max = 1024kb
100.14s real 12.06s system 3.16s user 170865+13406 cs diff -r $NFSDIR $NFSDIR2
SERIALIZED, BIG FILES
=====================
readahead_ratio = 0, ra_max = 128kb
56.52s real 3.38s system 1.23s user 47930+5256 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb
32.54s real 5.71s system 1.38s user 23851+17007 cs diff $NFSFILE $NFSFILE2
PARALLEL, BIG FILES
===================
readahead_ratio = 0, ra_max = 128kb
63.35s real 5.68s system 1.57s user 82594+48747 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb
33.87s real 10.17s system 1.55s user 72291+100079 cs diff $NFSFILE $NFSFILE2
Signed-off-by: Wu Fengguang <[email protected]>
---
fs/nfsd/vfs.c | 6 +++++-
include/linux/fs.h | 1 +
mm/readahead.c | 11 +++++++++--
3 files changed, 15 insertions(+), 3 deletions(-)
--- linux.orig/fs/nfsd/vfs.c
+++ linux/fs/nfsd/vfs.c
@@ -832,10 +832,14 @@ nfsd_vfs_read(struct svc_rqst *rqstp, st
#endif
/* Get readahead parameters */
- ra = nfsd_get_raparms(inode->i_sb->s_dev, inode->i_ino);
+ if (prefer_adaptive_readahead())
+ ra = NULL;
+ else
+ ra = nfsd_get_raparms(inode->i_sb->s_dev, inode->i_ino);
if (ra && ra->p_set)
file->f_ra = ra->p_ra;
+ file->f_ra.flags |= RA_FLAG_NFSD;
if (file->f_op->sendfile) {
svc_pushback_unused_pages(rqstp);
--- linux.orig/include/linux/fs.h
+++ linux/include/linux/fs.h
@@ -632,6 +632,7 @@ struct file_ra_state {
#define RA_FLAG_INCACHE 0x02 /* file is already in cache */
#define RA_FLAG_MMAP (1UL<<31) /* mmaped page access */
#define RA_FLAG_NO_LOOKAHEAD (1UL<<30) /* disable look-ahead */
+#define RA_FLAG_NFSD (1UL<<29) /* request from nfsd */
struct file {
/*
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -15,11 +15,13 @@
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>
+#include <linux/nfsd/const.h>
/* The default max/min read-ahead pages. */
#define KB(size) (((size)*1024 + PAGE_CACHE_SIZE-1) / PAGE_CACHE_SIZE)
#define MAX_RA_PAGES KB(VM_MAX_READAHEAD)
#define MIN_RA_PAGES KB(VM_MIN_READAHEAD)
+#define MIN_NFSD_PAGES KB(NFSSVC_MAXBLKSIZE/1024)
/* In laptop mode, poll delayed look-ahead on every ## pages read. */
#define LAPTOP_POLL_INTERVAL 16
@@ -1791,8 +1793,13 @@ newfile_readahead(struct address_space *
if (req_size > ra_min)
req_size = ra_min;
- ra_size = 4 * req_size;
- la_size = 2 * req_size;
+ if (unlikely(ra->flags & RA_FLAG_NFSD)) {
+ ra_size = MIN_NFSD_PAGES;
+ la_size = 0;
+ } else {
+ ra_size = 4 * req_size;
+ la_size = 2 * req_size;
+ }
ra_set_class(ra, RA_CLASS_NEWFILE);
ra_set_index(ra, 0, 0);
--
On Fri, Dec 16, 2005 at 09:07:49PM +0800, Wu Fengguang wrote:
> ------------------------------------------------------------------------
> Here is some test output(8 nfsd; local mount with tcp,rsize=8192):
What are the numbers when you use a more realistic rsize like 32768?
Greg.
--
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.
On Sat, Dec 17, 2005 at 11:05:22AM +1100, Greg Banks wrote:
> On Fri, Dec 16, 2005 at 09:07:49PM +0800, Wu Fengguang wrote:
> > ------------------------------------------------------------------------
> > Here is some test output(8 nfsd; local mount with tcp,rsize=8192):
>
> What are the numbers when you use a more realistic rsize like 32768?
Here they are. The normal data are now much better, and come close to that of
the serialized ones.
NORMAL
readahead_ratio = 8, ra_max = 1024kb (old logic)
48.36s real 2.22s system 1.51s user 7209+4110 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb (new logic)
30.04s real 2.46s system 1.33s user 5420+2492 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 8, ra_max = 1024kb
92.99s real 10.32s system 3.23s user 145004+1826 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
readahead_ratio = 70, ra_max = 1024kb
90.96s real 10.68s system 3.22s user 144414+2520 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
SERIALIZED
readahead_ratio = 8, ra_max = 1024kb
47.58s real 2.10s system 1.27s user 7933+1357 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 70, ra_max = 1024kb
29.46s real 2.41s system 1.38s user 5590+2613 cs diff $NFSFILE $NFSFILE2
readahead_ratio = 8, ra_max = 1024kb
93.02s real 10.67s system 3.25s user 144850+2286 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
readahead_ratio = 70, ra_max = 1024kb
91.15s real 11.04s system 3.31s user 144432+2814 cs diff -r $NFSDIR $NFSDIR2 > /dev/null
Regards,
Wu