Hi Rasmus,
On Sun, Oct 4, 2015 at 9:09 AM, Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:
> 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
Quick question:
> 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;
You don't seem to be accounting for the null bytes here.
Thanks,
--
Julian Calaby
Email: julian.calaby@xxxxxxxxx
Profile: http://www.google.com/profiles/julian.calaby/
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