From: Jens Axboe <jens.axboe@xxxxxxxxxx>
Subject: Re: [RFC 4/8] scsi-ml: scsi_sgtable implementation
Date: Wed, 18 Jul 2007 22:17:10 +0200
> On Wed, Jul 18 2007, Benny Halevy wrote:
> > Jens Axboe wrote:
> > > On Wed, Jul 18 2007, Boaz Harrosh wrote:
> > >> Jens Axboe wrote:
> > >>> On Wed, Jul 18 2007, Boaz Harrosh wrote:
> > >>>> FUJITA Tomonori wrote:
> > >>>>> From: Mike Christie <michaelc@xxxxxxxxxxx>
> > >>>>> Subject: Re: [RFC 4/8] scsi-ml: scsi_sgtable implementation
> > >>>>> Date: Thu, 12 Jul 2007 14:09:44 -0500
> > >>>>>
> > >>>>>> Boaz Harrosh wrote:
> > >>>>>>> +/*
> > >>>>>>> + * Should fit within a single page.
> > >>>>>>> + */
> > >>>>>>> +enum { SCSI_MAX_SG_SEGMENTS =
> > >>>>>>> + ((PAGE_SIZE - sizeof(struct scsi_sgtable)) /
> > >>>>>>> + sizeof(struct scatterlist)) };
> > >>>>>>> +
> > >>>>>>> +enum { SG_MEMPOOL_NR =
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 7) +
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 15) +
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 31) +
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 63) +
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 127) +
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 255) +
> > >>>>>>> + (SCSI_MAX_SG_SEGMENTS >= 511)
> > >>>>>>> +};
> > >>>>>>>
> > >>>>>> What does SCSI_MAX_SG_SEGMENTS end up being on x86 now? On x86_64 or
> > >>>>>> some other arch, we were going over a page when doing
> > >>>>>> SCSI_MAX_PHYS_SEGMENTS of 256 right?
> > >>>>> Seems that 170 with x86 and 127 with x86_64.
> > >>>>>
> > >>>> with scsi_sgtable we get one less than now
> > >>>>
> > >>>> Arch | SCSI_MAX_SG_SEGMENTS = | sizeof(struct scatterlist)
> > >>>> --------------------------|-------------------------|---------------------------
> > >>>> x86_64 | 127 |32
> > >>>> i386 CONFIG_HIGHMEM64G=y | 204 |20
> > >>>> i386 other | 255 |16
> > >>>>
> > >>>> What's nice about this code is that now finally it is
> > >>>> automatically calculated in compile time. Arch people
> > >>>> don't have the headache "did I break SCSI-ml?".
> > >>>> For example observe the current bug with i386
> > >>>> CONFIG_HIGHMEM64G=y.
> > >>>>
> > >>>> The same should be done with BIO's. Than ARCHs with big
> > >>>> pages can gain even more.
> > >>>>
> > >>>>>> What happened to Jens's scatter list chaining and how does this relate
> > >>>>>> to it then?
> > >>>>> With Jens' sglist, we can set SCSI_MAX_SG_SEGMENTS to whatever we
> > >>>>> want. We can remove the above code.
> > >>>>>
> > >>>>> We need to push this and Jens' sglist together in one merge window, I
> > >>>>> think.
> > >>>> No Tomo the above does not go away. What goes away is maybe:
> > >>> It does go away, since we can just set it to some safe value and use
> > >>> chaining to get us where we want.
> > >> In my patches SCSI_MAX_PHYS_SEGMENTS has went away it does not exist
> > >> anymore.
> > >
> > > Sure, I could just kill it as well. The point is that it's a parallel
> > > development, there's nothing in your patch that helps the sg chaining
> > > whatsoever. The only "complex" thing in the SCSI layer for sg chaining,
> > > is chaining when allocating and walking that chain on freeing. That's
> > > it!
> >
> > It seems like having the pool index in the sgtable structure simplifies
> > the implementation a bit for allocation and freeing of linked sgtables.
> > Boaz will send an example tomorrow (hopefully) showing how the merged
> > code looks like.
>
> The index stuff isn't complex, so I don't think you can call that a real
> simplification. It's not for free either, there's a size cost to pay.
I think that the main issue of integrating sgtable and sglist is how
to put scatterlist to scsi_sgtable structure.
If we allocate a scsi_sgtable structure and sglists separately, the
code is pretty simple. But probably it's not the best way from the
perspective of performance.
If we put sglists into the scsi_sgtable structure (like Boaz's patch
does) and allocate and chain sglists only for large I/Os, we would
have the better performance (especially for small I/Os). But we will
have more complicated code.
I wrote my sgtable patch over Jens' sglist with the former way:
master.kernel.org:/pub/scm/linux/kernel/git/tomo/linux-2.6-bidi.git sgtable
I also put Boaz's scsi_error, sd, and sr sgtable patches into the tree
so you can try it. I've tested this with only normal size I/Os (not
tested sglist code). I don't touch the sglist code much, so hopefully
it works.
I've attached the sgtable patch for review. It's against the
sglist-arch branch in Jens' tree.
---
From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Subject: [PATCH] move all the I/O descriptors to a new scsi_sgtable structure
based on Boaz Harrosh <bharrosh@xxxxxxxxxxx> scsi_sgtable patch.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
---
drivers/scsi/scsi_lib.c | 92 +++++++++++++++++++++++++++------------------
include/scsi/scsi_cmnd.h | 39 +++++++++++++------
2 files changed, 82 insertions(+), 49 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5fb1048..2fa1852 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -52,6 +52,8 @@ static struct scsi_host_sg_pool scsi_sg_pools[] = {
};
#undef SP
+static struct kmem_cache *scsi_sgtable_cache;
+
static void scsi_run_queue(struct request_queue *q);
/*
@@ -731,16 +733,27 @@ static inline unsigned int scsi_sgtable_index(unsigned short nents)
return index;
}
-struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
+struct scsi_sgtable *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask,
+ int sg_count)
{
struct scsi_host_sg_pool *sgp;
struct scatterlist *sgl, *prev, *ret;
+ struct scsi_sgtable *sgt;
unsigned int index;
int this, left;
- BUG_ON(!cmd->use_sg);
+ sgt = kmem_cache_zalloc(scsi_sgtable_cache, gfp_mask);
+ if (!sgt)
+ return NULL;
+
+ /*
+ * don't allow subsequent mempool allocs to sleep, it would
+ * violate the mempool principle.
+ */
+ gfp_mask &= ~__GFP_WAIT;
+ gfp_mask |= __GFP_HIGH;
- left = cmd->use_sg;
+ left = sg_count;
ret = prev = NULL;
do {
this = left;
@@ -764,7 +777,7 @@ struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
* first loop through, set initial index and return value
*/
if (!ret) {
- cmd->sglist_len = index;
+ sgt->sglist_len = index;
ret = sgl;
}
@@ -776,21 +789,18 @@ struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
if (prev)
sg_chain(prev, SCSI_MAX_SG_SEGMENTS, sgl);
- /*
- * don't allow subsequent mempool allocs to sleep, it would
- * violate the mempool principle.
- */
- gfp_mask &= ~__GFP_WAIT;
- gfp_mask |= __GFP_HIGH;
prev = sgl;
} while (left);
/*
- * ->use_sg may get modified after dma mapping has potentially
+ * ->sg_count may get modified after dma mapping has potentially
* shrunk the number of segments, so keep a copy of it for free.
*/
- cmd->__use_sg = cmd->use_sg;
- return ret;
+ sgt->sg_count = sg_count;
+ sgt->__sg_count = sg_count;
+ sgt->sglist = ret;
+ cmd->sgtable = sgt;
+ return sgt;
enomem:
if (ret) {
/*
@@ -809,6 +819,8 @@ enomem:
mempool_free(prev, sgp->pool);
}
+ kmem_cache_free(scsi_sgtable_cache, sgt);
+
return NULL;
}
@@ -816,21 +828,22 @@ EXPORT_SYMBOL(scsi_alloc_sgtable);
void scsi_free_sgtable(struct scsi_cmnd *cmd)
{
- struct scatterlist *sgl = cmd->request_buffer;
+ struct scsi_sgtable *sgt = cmd->sgtable;
+ struct scatterlist *sgl = sgt->sglist;
struct scsi_host_sg_pool *sgp;
- BUG_ON(cmd->sglist_len >= SG_MEMPOOL_NR);
+ BUG_ON(sgt->sglist_len >= SG_MEMPOOL_NR);
/*
* if this is the biggest size sglist, check if we have
* chained parts we need to free
*/
- if (cmd->__use_sg > SCSI_MAX_SG_SEGMENTS) {
+ if (sgt->__sg_count > SCSI_MAX_SG_SEGMENTS) {
unsigned short this, left;
struct scatterlist *next;
unsigned int index;
- left = cmd->__use_sg - (SCSI_MAX_SG_SEGMENTS - 1);
+ left = sgt->__sg_count - (SCSI_MAX_SG_SEGMENTS - 1);
next = sg_chain_ptr(&sgl[SCSI_MAX_SG_SEGMENTS - 1]);
while (left && next) {
sgl = next;
@@ -854,11 +867,12 @@ void scsi_free_sgtable(struct scsi_cmnd *cmd)
/*
* Restore original, will be freed below
*/
- sgl = cmd->request_buffer;
+ sgl = sgt->sglist;
}
- sgp = scsi_sg_pools + cmd->sglist_len;
+ sgp = scsi_sg_pools + sgt->sglist_len;
mempool_free(sgl, sgp->pool);
+ kmem_cache_free(scsi_sgtable_cache, sgt);
}
EXPORT_SYMBOL(scsi_free_sgtable);
@@ -882,15 +896,14 @@ EXPORT_SYMBOL(scsi_free_sgtable);
*/
static void scsi_release_buffers(struct scsi_cmnd *cmd)
{
- if (cmd->use_sg)
+ if (cmd->sgtable)
scsi_free_sgtable(cmd);
/*
* Zero these out. They now point to freed memory, and it is
* dangerous to hang onto the pointers.
*/
- cmd->request_buffer = NULL;
- cmd->request_bufflen = 0;
+ cmd->sgtable = NULL;
}
/*
@@ -924,13 +937,14 @@ static void scsi_release_buffers(struct scsi_cmnd *cmd)
void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
{
int result = cmd->result;
- int this_count = cmd->request_bufflen;
+ int this_count = scsi_bufflen(cmd);
request_queue_t *q = cmd->device->request_queue;
struct request *req = cmd->request;
int clear_errors = 1;
struct scsi_sense_hdr sshdr;
int sense_valid = 0;
int sense_deferred = 0;
+ int resid = scsi_get_resid(cmd);
scsi_release_buffers(cmd);
@@ -956,7 +970,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
req->sense_len = len;
}
}
- req->data_len = cmd->resid;
+ req->data_len = resid;
}
/*
@@ -1098,6 +1112,7 @@ EXPORT_SYMBOL(scsi_io_completion);
static int scsi_init_io(struct scsi_cmnd *cmd)
{
struct request *req = cmd->request;
+ struct scsi_sgtable *sgt;
int count;
/*
@@ -1105,35 +1120,36 @@ static int scsi_init_io(struct scsi_cmnd *cmd)
* but now we do (it makes highmem I/O easier to support without
* kmapping pages)
*/
- cmd->use_sg = req->nr_phys_segments;
+ sgt = scsi_alloc_sgtable(cmd, GFP_ATOMIC, req->nr_phys_segments);
/*
* If sg table allocation fails, requeue request later.
*/
- cmd->request_buffer = scsi_alloc_sgtable(cmd, GFP_ATOMIC);
- if (unlikely(!cmd->request_buffer)) {
+ if (unlikely(!sgt)) {
scsi_unprep_request(req);
return BLKPREP_DEFER;
}
+ cmd->sgtable = sgt;
+
req->buffer = NULL;
if (blk_pc_request(req))
- cmd->request_bufflen = req->data_len;
+ sgt->length = req->data_len;
else
- cmd->request_bufflen = req->nr_sectors << 9;
+ sgt->length = req->nr_sectors << 9;
/*
* Next, walk the list, and fill in the addresses and sizes of
* each segment.
*/
- count = blk_rq_map_sg(req->q, req, cmd->request_buffer);
- if (likely(count <= cmd->use_sg)) {
- cmd->use_sg = count;
+ count = blk_rq_map_sg(req->q, req, cmd->sgtable->sglist);
+ if (likely(count <= sgt->sg_count)) {
+ sgt->sg_count = count;
return BLKPREP_OK;
}
printk(KERN_ERR "Incorrect number of segments after building list\n");
- printk(KERN_ERR "counted %d, received %d\n", count, cmd->use_sg);
+ printk(KERN_ERR "counted %d, received %d\n", count, sgt->sg_count);
printk(KERN_ERR "req nr_sec %lu, cur_nr_sec %u\n", req->nr_sectors,
req->current_nr_sectors);
@@ -1189,7 +1205,7 @@ static void scsi_blk_pc_done(struct scsi_cmnd *cmd)
* successfully. Since this is a REQ_BLOCK_PC command the
* caller should check the request's errors value
*/
- scsi_io_completion(cmd, cmd->request_bufflen);
+ scsi_io_completion(cmd, scsi_bufflen(cmd));
}
static int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
@@ -1218,9 +1234,7 @@ static int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
BUG_ON(req->data_len);
BUG_ON(req->data);
- cmd->request_bufflen = 0;
- cmd->request_buffer = NULL;
- cmd->use_sg = 0;
+ cmd->sgtable = NULL;
req->buffer = NULL;
}
@@ -1786,6 +1800,10 @@ int __init scsi_init_queue(void)
return -ENOMEM;
}
+ scsi_sgtable_cache = kmem_cache_create("scsi_sgtable",
+ sizeof(struct scsi_sgtable),
+ 0, 0, NULL);
+
for (i = 0; i < SG_MEMPOOL_NR; i++) {
struct scsi_host_sg_pool *sgp = scsi_sg_pools + i;
int size = sgp->size * sizeof(struct scatterlist);
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index 937b3c4..9ead940 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -11,6 +11,14 @@ struct scatterlist;
struct Scsi_Host;
struct scsi_device;
+struct scsi_sgtable {
+ unsigned length;
+ int resid;
+ short sg_count;
+ short __sg_count;
+ short sglist_len;
+ struct scatterlist *sglist;
+};
/* embedded in scsi_cmnd */
struct scsi_pointer {
@@ -64,10 +72,9 @@ struct scsi_cmnd {
/* These elements define the operation we are about to perform */
#define MAX_COMMAND_SIZE 16
unsigned char cmnd[MAX_COMMAND_SIZE];
- unsigned request_bufflen; /* Actual request size */
struct timer_list eh_timeout; /* Used to time out the command. */
- void *request_buffer; /* Actual requested buffer */
+ struct scsi_sgtable *sgtable;
/* These elements define the operation we ultimately want to perform */
unsigned short use_sg; /* Number of pieces of scatter-gather */
@@ -83,10 +90,6 @@ struct scsi_cmnd {
reconnects. Probably == sector
size */
- int resid; /* Number of bytes requested to be
- transferred less actual number
- transferred (0 if not supported) */
-
struct request *request; /* The command we are
working on */
@@ -133,24 +136,36 @@ extern void *scsi_kmap_atomic_sg(struct scatterlist *sg, int sg_count,
size_t *offset, size_t *len);
extern void scsi_kunmap_atomic_sg(void *virt);
-extern struct scatterlist *scsi_alloc_sgtable(struct scsi_cmnd *, gfp_t);
+extern struct scsi_sgtable *scsi_alloc_sgtable(struct scsi_cmnd *, gfp_t, int);
extern void scsi_free_sgtable(struct scsi_cmnd *);
extern int scsi_dma_map(struct scsi_cmnd *cmd);
extern void scsi_dma_unmap(struct scsi_cmnd *cmd);
-#define scsi_sg_count(cmd) ((cmd)->use_sg)
-#define scsi_sglist(cmd) ((struct scatterlist *)(cmd)->request_buffer)
-#define scsi_bufflen(cmd) ((cmd)->request_bufflen)
+static inline unsigned scsi_sg_count(struct scsi_cmnd *cmd)
+{
+ return cmd->sgtable ? cmd->sgtable->sg_count : 0;
+}
+
+static inline struct scatterlist *scsi_sglist(struct scsi_cmnd *cmd)
+{
+ return cmd->sgtable ? cmd->sgtable->sglist : 0;
+}
+
+static inline unsigned scsi_bufflen(struct scsi_cmnd *cmd)
+{
+ return cmd->sgtable ? cmd->sgtable->length : 0;
+}
static inline void scsi_set_resid(struct scsi_cmnd *cmd, int resid)
{
- cmd->resid = resid;
+ if (cmd->sgtable)
+ cmd->sgtable->resid = resid;
}
static inline int scsi_get_resid(struct scsi_cmnd *cmd)
{
- return cmd->resid;
+ return cmd->sgtable ? cmd->sgtable->resid : 0;
}
#define scsi_for_each_sg(cmd, sg, nseg, __i) \
--
1.5.2.4
-
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