On Sat, Oct 03 2015, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> Hi Rasmus,
>
> I like this idea. But maybe it's also time to just move the constants
> to a plain text file and auto-generate C headers from them? That way
> the format in which they can be edited is decoupled from the
> representation in the kernel image.
Well, I don't really have an opinion on that part.
In the meantime, I got another idea for doubling the saving to 8k. It
requires a few more code changes and is perhaps also more hacky. 2/2
would be something like below. Please let me know which version you'd
prefer, and I'll send both patches properly.
Thanks,
Rasmus
Subject: [PATCH 2/2] scsi: reduce CONFIG_SCSI_CONSTANTS=y impact by 8k
On 64 bit, struct error_info has 6 bytes of padding, which amounts to
over 4k of wasted space in the additional[] array. We could easily get
rid of that by instead using separate arrays for the codes and the
pointers. However, we can do even better than that and save an
additional 6 bytes per entry: In the table, just store the sizeof()
the corresponding string literal. The cumulative sum of these is then
the appropriate offset into additional_text, which is built from the
concatenation (with '\0's inbetween) of the strings.
$ scripts/bloat-o-meter /tmp/vmlinux vmlinux
add/remove: 0/0 grow/shrink: 1/1 up/down: 24/-8488 (-8464)
function old new delta
scsi_extd_sense_format 136 160 +24
additional 11312 2824 -8488
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
drivers/scsi/constants.c | 25 +++++++++++++++++++++----
drivers/scsi/sense_codes.h | 2 --
2 files changed, 21 insertions(+), 6 deletions(-)
diff --git a/drivers/scsi/constants.c b/drivers/scsi/constants.c
index 47aaccd5e68e..ccd34b0481cd 100644
--- a/drivers/scsi/constants.c
+++ b/drivers/scsi/constants.c
@@ -292,17 +292,31 @@ bool scsi_opcode_sa_name(int opcode, int service_action,
struct error_info {
unsigned short code12; /* 0x0302 looks better than 0x03,0x02 */
- const char * text;
+ unsigned short size;
};
+/*
+ * There are 700+ entries in this table. To save space, we don't store
+ * (code, pointer) pairs, which would make sizeof(struct
+ * error_info)==16 on 64 bits. Rather, the second element just stores
+ * the size (including \0) of the corresponding string, and we use the
+ * sum of these to get the appropriate offset into additional_text
+ * defined below. This approach saves 12 bytes per entry.
+ */
static const struct error_info additional[] =
{
-#define SENSE_CODE(c, s) {c, s},
+#define SENSE_CODE(c, s) {c, sizeof(s)},
#include "sense_codes.h"
#undef SENSE_CODE
};
+static const char *additional_text =
+#define SENSE_CODE(c, s) s "\0"
+#include "sense_codes.h"
+#undef SENSE_CODE
+ ;
+
struct error_info2 {
unsigned char code1, code2_min, code2_max;
const char * str;
@@ -364,11 +378,14 @@ scsi_extd_sense_format(unsigned char asc, unsigned char ascq, const char **fmt)
{
int i;
unsigned short code = ((asc << 8) | ascq);
+ unsigned offset = 0;
*fmt = NULL;
- for (i = 0; additional[i].text; i++)
+ for (i = 0; i < ARRAY_SIZE(additional); i++) {
if (additional[i].code12 == code)
- return additional[i].text;
+ return additional_text + offset;
+ offset += additional[i].size;
+ }
for (i = 0; additional2[i].fmt; i++) {
if (additional2[i].code1 == asc &&
ascq >= additional2[i].code2_min &&
diff --git a/drivers/scsi/sense_codes.h b/drivers/scsi/sense_codes.h
index 54b3939d6309..da84d53b3379 100644
--- a/drivers/scsi/sense_codes.h
+++ b/drivers/scsi/sense_codes.h
@@ -833,5 +833,3 @@ SENSE_CODE(0x746E, "External data encryption control timeout")
SENSE_CODE(0x746F, "External data encryption control error")
SENSE_CODE(0x7471, "Logical unit access not authorized")
SENSE_CODE(0x7479, "Security conflict in translated device")
-
-SENSE_CODE(0, NULL)
--
--
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