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SubjectRe: [PATCH][resend][SCSI] Reduce number of sequential pointer derefs in scsi_error.c and reduce size as well
On Thu, 18 Nov 2010, Linus Torvalds wrote:

> On Thu, Nov 18, 2010 at 11:30 AM, Jesper Juhl <jj@chaosbits.net> wrote:
> >
> > This is the fourth time I send this patch. For some reason it seems unable
> > to get any feedback at all. I'd really appreciate a clear ACK or NACK on
> > it and I'll keep resending it until it's either merged or I get a NACK
> > with a reason.
>
> The patch looks ok to me, but you've basically selected the least
> interesting file possible. No wonder people can't seem to care.
>

Thank you very much for reviewing the patch and replying with your
feedback!

I agree that this is not the most sexy file in the tree to be modifying,
but I'm not seeking fame and fortune by doing this, just trying to
optimize the few corners I find - every little bit helps; right?


> Also, this is just ugly as hell, and doesn't help anything:
>
> + int (*eh_abort_handler)(struct scsi_cmnd *) =
> + scmd->device->host->hostt->eh_abort_handler;
>
> since the compiler will have optimized that double access away anyway
> (no writes in between). So you could have made it about a thousand
> times more readable with no downside by doing
>
> struct scsi_host_template *hostt = scmd->device->host->hostt;
>
> if (!hostt->eh_abort_handler)
> return FAILED;
> return hostt->eh_abort_handler(scmd);
>
> instead. Look ma, no long lines.
>
> Rule of thumb: if you need more than one line for an expression or
> variable definition, you're doing something wrong.
>

Fair enough. Seeing your version of this and looking a second time at mine
I have to agree completely.
You are absolutely right in stating that the compiler will handle this
just fine, so it's only a readabillity issue and your version is a *lot*
more readable than what I came up with.

I've updated the patch below - the original changelog bit still applies,
only change is what you pointed out above.


Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
scsi_error.c | 87 +++++++++++++++++++++++++++++++----------------------------
1 file changed, 46 insertions(+), 41 deletions(-)
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 824b8fc..8dc02c6 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -3,14 +3,14 @@
*
* SCSI error/timeout handling
* Initial versions: Eric Youngdale. Based upon conversations with
- * Leonard Zubkoff and David Miller at Linux Expo,
+ * Leonard Zubkoff and David Miller at Linux Expo,
* ideas originating from all over the place.
*
* Restructured scsi_unjam_host and associated functions.
* September 04, 2002 Mike Anderson (andmike@us.ibm.com)
*
* Forward port of Russell King's (rmk@arm.linux.org.uk) changes and
- * minor cleanups.
+ * minor cleanups.
* September 30, 2002 Mike Anderson (andmike@us.ibm.com)
*/

@@ -129,14 +129,15 @@ enum blk_eh_timer_return scsi_times_out(struct request *req)
{
struct scsi_cmnd *scmd = req->special;
enum blk_eh_timer_return rtn = BLK_EH_NOT_HANDLED;
+ struct Scsi_Host *host = scmd->device->host;

trace_scsi_dispatch_cmd_timeout(scmd);
scsi_log_completion(scmd, TIMEOUT_ERROR);

- if (scmd->device->host->transportt->eh_timed_out)
- rtn = scmd->device->host->transportt->eh_timed_out(scmd);
- else if (scmd->device->host->hostt->eh_timed_out)
- rtn = scmd->device->host->hostt->eh_timed_out(scmd);
+ if (host->transportt->eh_timed_out)
+ rtn = host->transportt->eh_timed_out(scmd);
+ else if (host->hostt->eh_timed_out)
+ rtn = host->hostt->eh_timed_out(scmd);

if (unlikely(rtn == BLK_EH_NOT_HANDLED &&
!scsi_eh_scmd_add(scmd, SCSI_EH_CANCEL_CMD))) {
@@ -195,7 +196,7 @@ static inline void scsi_eh_prt_fail_stats(struct Scsi_Host *shost,
++total_failures;
if (scmd->eh_eflags & SCSI_EH_CANCEL_CMD)
++cmd_cancel;
- else
+ else
++cmd_failed;
}
}
@@ -294,7 +295,7 @@ static int scsi_check_sense(struct scsi_cmnd *scmd)
return NEEDS_RETRY;
}
/*
- * if the device is in the process of becoming ready, we
+ * if the device is in the process of becoming ready, we
* should retry.
*/
if ((sshdr.asc == 0x04) && (sshdr.ascq == 0x01))
@@ -507,22 +508,23 @@ static int scsi_try_host_reset(struct scsi_cmnd *scmd)
{
unsigned long flags;
int rtn;
+ struct Scsi_Host *host = scmd->device->host;
+ struct scsi_host_template *hostt = host->hostt;

SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Snd Host RST\n",
__func__));

- if (!scmd->device->host->hostt->eh_host_reset_handler)
+ if (!hostt->eh_host_reset_handler)
return FAILED;

- rtn = scmd->device->host->hostt->eh_host_reset_handler(scmd);
+ rtn = hostt->eh_host_reset_handler(scmd);

if (rtn == SUCCESS) {
- if (!scmd->device->host->hostt->skip_settle_delay)
+ if (!hostt->skip_settle_delay)
ssleep(HOST_RESET_SETTLE_TIME);
- spin_lock_irqsave(scmd->device->host->host_lock, flags);
- scsi_report_bus_reset(scmd->device->host,
- scmd_channel(scmd));
- spin_unlock_irqrestore(scmd->device->host->host_lock, flags);
+ spin_lock_irqsave(host->host_lock, flags);
+ scsi_report_bus_reset(host, scmd_channel(scmd));
+ spin_unlock_irqrestore(host->host_lock, flags);
}

return rtn;
@@ -536,22 +538,23 @@ static int scsi_try_bus_reset(struct scsi_cmnd *scmd)
{
unsigned long flags;
int rtn;
+ struct Scsi_Host *host = scmd->device->host;
+ struct scsi_host_template *hostt = host->hostt;

SCSI_LOG_ERROR_RECOVERY(3, printk("%s: Snd Bus RST\n",
__func__));

- if (!scmd->device->host->hostt->eh_bus_reset_handler)
+ if (!hostt->eh_bus_reset_handler)
return FAILED;

- rtn = scmd->device->host->hostt->eh_bus_reset_handler(scmd);
+ rtn = hostt->eh_bus_reset_handler(scmd);

if (rtn == SUCCESS) {
- if (!scmd->device->host->hostt->skip_settle_delay)
+ if (!hostt->skip_settle_delay)
ssleep(BUS_RESET_SETTLE_TIME);
- spin_lock_irqsave(scmd->device->host->host_lock, flags);
- scsi_report_bus_reset(scmd->device->host,
- scmd_channel(scmd));
- spin_unlock_irqrestore(scmd->device->host->host_lock, flags);
+ spin_lock_irqsave(host->host_lock, flags);
+ scsi_report_bus_reset(host, scmd_channel(scmd));
+ spin_unlock_irqrestore(host->host_lock, flags);
}

return rtn;
@@ -577,16 +580,18 @@ static int scsi_try_target_reset(struct scsi_cmnd *scmd)
{
unsigned long flags;
int rtn;
+ struct Scsi_Host *host = scmd->device->host;
+ struct scsi_host_template *hostt = host->hostt;

- if (!scmd->device->host->hostt->eh_target_reset_handler)
+ if (!hostt->eh_target_reset_handler)
return FAILED;

- rtn = scmd->device->host->hostt->eh_target_reset_handler(scmd);
+ rtn = hostt->eh_target_reset_handler(scmd);
if (rtn == SUCCESS) {
- spin_lock_irqsave(scmd->device->host->host_lock, flags);
+ spin_lock_irqsave(host->host_lock, flags);
__starget_for_each_device(scsi_target(scmd->device), NULL,
__scsi_report_device_reset);
- spin_unlock_irqrestore(scmd->device->host->host_lock, flags);
+ spin_unlock_irqrestore(host->host_lock, flags);
}

return rtn;
@@ -605,11 +610,12 @@ static int scsi_try_target_reset(struct scsi_cmnd *scmd)
static int scsi_try_bus_device_reset(struct scsi_cmnd *scmd)
{
int rtn;
+ struct scsi_host_template *hostt = scmd->device->host->hostt;

- if (!scmd->device->host->hostt->eh_device_reset_handler)
+ if (!hostt->eh_device_reset_handler)
return FAILED;

- rtn = scmd->device->host->hostt->eh_device_reset_handler(scmd);
+ rtn = hostt->eh_device_reset_handler(scmd);
if (rtn == SUCCESS)
__scsi_report_device_reset(scmd->device, NULL);
return rtn;
@@ -617,10 +623,10 @@ static int scsi_try_bus_device_reset(struct scsi_cmnd *scmd)

static int __scsi_try_to_abort_cmd(struct scsi_cmnd *scmd)
{
- if (!scmd->device->host->hostt->eh_abort_handler)
- return FAILED;
-
- return scmd->device->host->hostt->eh_abort_handler(scmd);
+ struct scsi_host_template *hostt = scmd->device->host->hostt;
+ if (!hostt->eh_abort_handler)
+ return FAILED;
+ return hostt->eh_abort_handler(scmd);
}

/**
@@ -867,7 +873,7 @@ EXPORT_SYMBOL(scsi_eh_finish_cmd);
*
* Description:
* See if we need to request sense information. if so, then get it
- * now, so we have a better idea of what to do.
+ * now, so we have a better idea of what to do.
*
* Notes:
* This has the unfortunate side effect that if a shost adapter does
@@ -987,7 +993,6 @@ static int scsi_eh_abort_cmds(struct list_head *work_q,
!scsi_eh_tur(scmd)) {
scsi_eh_finish_cmd(scmd, done_q);
}
-
} else
SCSI_LOG_ERROR_RECOVERY(3, printk("%s: aborting"
" cmd failed:"
@@ -1031,7 +1036,7 @@ static int scsi_eh_try_stu(struct scsi_cmnd *scmd)
*
* Notes:
* If commands are failing due to not ready, initializing command required,
- * try revalidating the device, which will end up sending a start unit.
+ * try revalidating the device, which will end up sending a start unit.
*/
static int scsi_eh_stu(struct Scsi_Host *shost,
struct list_head *work_q,
@@ -1085,7 +1090,7 @@ static int scsi_eh_stu(struct Scsi_Host *shost,
* Try a bus device reset. Still, look to see whether we have multiple
* devices that are jammed or not - if we have multiple devices, it
* makes no sense to try bus_device_reset - we really would need to try
- * a bus_reset instead.
+ * a bus_reset instead.
*/
static int scsi_eh_bus_device_reset(struct Scsi_Host *shost,
struct list_head *work_q,
@@ -1196,7 +1201,7 @@ static int scsi_eh_target_reset(struct Scsi_Host *shost,
}

/**
- * scsi_eh_bus_reset - send a bus reset
+ * scsi_eh_bus_reset - send a bus reset
* @shost: &scsi host being recovered.
* @work_q: &list_head for pending commands.
* @done_q: &list_head for processed commands.
@@ -1213,7 +1218,7 @@ static int scsi_eh_bus_reset(struct Scsi_Host *shost,
* we really want to loop over the various channels, and do this on
* a channel by channel basis. we should also check to see if any
* of the failed commands are on soft_reset devices, and if so, skip
- * the reset.
+ * the reset.
*/

for (channel = 0; channel <= shost->max_channel; channel++) {
@@ -1255,7 +1260,7 @@ static int scsi_eh_bus_reset(struct Scsi_Host *shost,
}

/**
- * scsi_eh_host_reset - send a host reset
+ * scsi_eh_host_reset - send a host reset
* @work_q: list_head for processed commands.
* @done_q: list_head for processed commands.
*/
@@ -1408,7 +1413,7 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd)
return SUCCESS;
/*
* when the low level driver returns did_soft_error,
- * it is responsible for keeping an internal retry counter
+ * it is responsible for keeping an internal retry counter
* in order to avoid endless loops (db)
*
* actually this is a bug in this function here. we should
@@ -2005,7 +2010,7 @@ int scsi_normalize_sense(const u8 *sense_buffer, int sb_len,
if (sb_len > 7)
sshdr->additional_length = sense_buffer[7];
} else {
- /*
+ /*
* fixed format
*/
if (sb_len > 2)


--
Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.



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