* [PATCH][SCSI]: Save some bytes in struct scsi_target
@ 2006-12-12 3:17 Arnaldo Carvalho de Melo
2006-12-12 3:52 ` Matthew Wilcox
0 siblings, 1 reply; 3+ messages in thread
From: Arnaldo Carvalho de Melo @ 2006-12-12 3:17 UTC (permalink / raw)
To: James E.J. Bottomley; +Cc: Andrew Morton, linux-scsi, linux-kernel
Before:
[acme@newtoy kpahole-2.6]$ pahole --cacheline 32 /tmp/scsi.o.before scsi_target
/* include/scsi/scsi_device.h:86 */
struct scsi_target {
struct scsi_device * starget_sdev_user; /* 0 4 */
struct list_head siblings; /* 4 8 */
struct list_head devices; /* 12 8 */
struct device dev; /* 20 300 */
/* --- cacheline 10 boundary (320 bytes) --- */
unsigned int reap_ref; /* 320 4 */
unsigned int channel; /* 324 4 */
unsigned int id; /* 328 4 */
unsigned int create:1; /* 332 4 */
/* XXX 31 bits hole, try to pack */
unsigned int pdt_1f_for_no_lun; /* 336 4 */
char scsi_level; /* 340 1 */
/* XXX 3 bytes hole, try to pack */
struct execute_work ew; /* 344 16 */
/* --- cacheline 11 boundary (352 bytes) was 8 bytes ago --- */
enum scsi_target_state state; /* 360 4 */
void * hostdata; /* 364 4 */
long unsigned int starget_data[0]; /* 368 0 */
}; /* size: 368, cachelines: 12 */
/* sum members: 365, holes: 1, sum holes: 3 */
/* bit holes: 1, sum bit holes: 31 bits */
/* last cacheline: 16 bytes */
After:
[acme@newtoy kpahole-2.6]$ pahole --cacheline 32 drivers/scsi/scsi.o scsi_target
/* include/scsi/scsi_device.h:86 */
struct scsi_target {
struct scsi_device * starget_sdev_user; /* 0 4 */
struct list_head siblings; /* 4 8 */
struct list_head devices; /* 12 8 */
struct device dev; /* 20 300 */
/* --- cacheline 10 boundary (320 bytes) --- */
unsigned int reap_ref; /* 320 4 */
unsigned int channel; /* 324 4 */
unsigned int id; /* 328 4 */
char scsi_level; /* 332 1 */
unsigned char create:1; /* 333 1 */
/* XXX 7 bits hole, try to pack */
/* XXX 2 bytes hole, try to pack */
unsigned int pdt_1f_for_no_lun; /* 336 4 */
struct execute_work ew; /* 340 16 */
/* --- cacheline 11 boundary (352 bytes) was 4 bytes ago --- */
enum scsi_target_state state; /* 356 4 */
void * hostdata; /* 360 4 */
long unsigned int starget_data[0]; /* 364 0 */
}; /* size: 364, cachelines: 12 */
/* sum members: 362, holes: 1, sum holes: 2 */
/* bit holes: 1, sum bit holes: 7 bits */
/* last cacheline: 12 bytes */
[acme@newtoy kpahole-2.6]$ codiff -V /tmp/scsi.o.before drivers/scsi/scsi.o
drivers/scsi/scsi.c:
struct scsi_target | -4
create:1;
from: unsigned int /* 332(31) 4(1) */
to: unsigned char /* 333(7) 1(1) */
scsi_level;
from: char /* 340(0) 1(0) */
to: char /* 332(0) 1(0) */
<SNIP offset changes>
1 struct changed
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
---
scsi_device.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index ebf31b1..ab245fc 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -175,11 +175,11 @@ struct scsi_target {
unsigned int channel;
unsigned int id; /* target id ... replace
* scsi_device.id eventually */
- unsigned int create:1; /* signal that it needs to be added */
+ char scsi_level;
+ unsigned char create:1; /* signal that it needs to be added */
unsigned int pdt_1f_for_no_lun; /* PDT = 0x1f */
/* means no lun present */
- char scsi_level;
struct execute_work ew;
enum scsi_target_state state;
void *hostdata; /* available to low-level driver */
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH][SCSI]: Save some bytes in struct scsi_target 2006-12-12 3:17 [PATCH][SCSI]: Save some bytes in struct scsi_target Arnaldo Carvalho de Melo @ 2006-12-12 3:52 ` Matthew Wilcox 2006-12-12 4:17 ` Arnaldo Carvalho de Melo 0 siblings, 1 reply; 3+ messages in thread From: Matthew Wilcox @ 2006-12-12 3:52 UTC (permalink / raw) To: Arnaldo Carvalho de Melo Cc: James E.J. Bottomley, Andrew Morton, linux-scsi, linux-kernel On Tue, Dec 12, 2006 at 01:17:18AM -0200, Arnaldo Carvalho de Melo wrote: > }; /* size: 368, cachelines: 12 */ > }; /* size: 364, cachelines: 12 */ Saving space is always good ;-) > - unsigned int create:1; /* signal that it needs to be added */ > + char scsi_level; > + unsigned char create:1; /* signal that it needs to be added */ > unsigned int pdt_1f_for_no_lun; /* PDT = 0x1f */ > /* means no lun present */ > > - char scsi_level; However, pdt_1f_for_no_lun is really only one bit, saving another 4 bytes. > struct execute_work ew; > enum scsi_target_state state; enums are a bit of a pain. Even though scsi_target_state uses only two values, it's represented as an int. Unless you're on arm-eabi, when it'll use less. And even then, it won't use less than a byte, as it has to be addressable. I wonder if we can turn scsi_target_state into a bit. That'll save another 8 bytes total. ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH][SCSI]: Save some bytes in struct scsi_target 2006-12-12 3:52 ` Matthew Wilcox @ 2006-12-12 4:17 ` Arnaldo Carvalho de Melo 0 siblings, 0 replies; 3+ messages in thread From: Arnaldo Carvalho de Melo @ 2006-12-12 4:17 UTC (permalink / raw) To: Matthew Wilcox Cc: James E.J. Bottomley, Andrew Morton, linux-scsi, linux-kernel On Mon, Dec 11, 2006 at 08:52:22PM -0700, Matthew Wilcox wrote: > On Tue, Dec 12, 2006 at 01:17:18AM -0200, Arnaldo Carvalho de Melo wrote: > > }; /* size: 368, cachelines: 12 */ > > }; /* size: 364, cachelines: 12 */ > > Saving space is always good ;-) > > > - unsigned int create:1; /* signal that it needs to be added */ > > + char scsi_level; > > + unsigned char create:1; /* signal that it needs to be added */ > > unsigned int pdt_1f_for_no_lun; /* PDT = 0x1f */ > > /* means no lun present */ > > > > - char scsi_level; > > However, pdt_1f_for_no_lun is really only one bit, saving another 4 bytes. > > > struct execute_work ew; > > enum scsi_target_state state; > > enums are a bit of a pain. Even though scsi_target_state uses only two > values, it's represented as an int. Unless you're on arm-eabi, when > it'll use less. And even then, it won't use less than a byte, as it has > to be addressable. I wonder if we can turn scsi_target_state into a > bit. That'll save another 8 bytes total. I guess we could use: enum scsi_target_state state:1; And make the enum entries start with 0 and not 1 as is today, no? With that we get down to: }; /* size: 356, cachelines: 12 */ /* last cacheline: 4 bytes */ Anything else to save these 4 bytes and get down to 11 cachelines per scsi_target instance? Following patch is on top of the previous one. Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index ab245fc..772f834 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -157,7 +157,7 @@ #define scmd_printk(prefix, scmd, fmt, a dev_printk(prefix, &(scmd)->device->sdev_gendev, fmt, ##a) enum scsi_target_state { - STARGET_RUNNING = 1, + STARGET_RUNNING = 0, STARGET_DEL, }; @@ -176,12 +176,12 @@ struct scsi_target { unsigned int id; /* target id ... replace * scsi_device.id eventually */ char scsi_level; + enum scsi_target_state state:1; unsigned char create:1; /* signal that it needs to be added */ - unsigned int pdt_1f_for_no_lun; /* PDT = 0x1f */ + unsigned char pdt_1f_for_no_lun:1; /* PDT = 0x1f */ /* means no lun present */ struct execute_work ew; - enum scsi_target_state state; void *hostdata; /* available to low-level driver */ unsigned long starget_data[0]; /* for the transport */ /* starget_data must be the last element!!!! */ ^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2006-12-12 13:26 UTC | newest] Thread overview: 3+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2006-12-12 3:17 [PATCH][SCSI]: Save some bytes in struct scsi_target Arnaldo Carvalho de Melo 2006-12-12 3:52 ` Matthew Wilcox 2006-12-12 4:17 ` Arnaldo Carvalho de Melo
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