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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, Jesper Juhl wrote:

> 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.
>
Aww crap, emacs just screwed me over on this one - that'll teach me to
keep my .emacs files in sync across machines. Sorry about that, the
previous mail used spaces for indentation not tabs - this should be
better:

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
scsi_error.c | 85 +++++++++++++++++++++++++++++++----------------------------
1 file changed, 45 insertions(+), 40 deletions(-)
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 824b8fc..ef89f3f 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)
+ struct scsi_host_template *hostt = scmd->device->host->hostt;
+ if (!hostt->eh_abort_handler)
return FAILED;
-
- return scmd->device->host->hostt->eh_abort_handler(scmd);
+ 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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