rtc: cmos: avoid taking rtc_lock for extended period of time
PATCH 1/1 rtc: cmos: avoid taking rtc_lock for extended period of time
On my device reading entirety of /sys/devices/pnp0/00:03/cmos_nvram0/nvmem takes about 9 msec during which time interrupts are off on the CPU that does the read and the thread that performs the read can not be migrated or preempted by another higher priority thread (RT or not).
Allow readers and writers be preempted by taking and releasing rtc_lock spinlock for each individual byte read or written rather than once per read/write request.
--- drivers/rtc/rtc-cmos.c | 31 +++++++++++++++---------------- 1 file changed, 15 insertions(+), 16 deletions(-)
drivers/rtc/rtc-cmos.c +15 -16
@@ -645,18 +645,17 @@ static int cmos_nvram_read(void *priv, unsigned int off, void *val,unsigned char *buf = val; off +=NVRAM_OFFSET ; -spin_lock_irq (&rtc_lock); -for (; count; count--, off++) { +for (; count; count--, off++, buf++) { +guard (spinlock_irq)(&rtc_lock);if (off <128 ) - *buf++ =CMOS_READ (off); + *buf =CMOS_READ (off);else if (can_bank2) - *buf++ =cmos_read_bank2 (off); + *buf =cmos_read_bank2 (off);else -break ; +return -EIO ; } -spin_unlock_irq (&rtc_lock); -return count ? -EIO :0 ; +return count; } static int cmos_nvram_write(void *priv, unsigned int off, void *val,
@@ -671,23 +670,23 @@ static int cmos_nvram_write(void *priv, unsigned int off, void *val,* NVRAM to update, updating checksums is also part of its job. */ off +=NVRAM_OFFSET ; -spin_lock_irq (&rtc_lock); -for (; count; count--, off++) { +for (; count; count--, off++, buf++) {/* don't trash RTC registers */ if (off == cmos->day_alrm || off == cmos->mon_alrm || off == cmos->century) - buf++; -else if (off <128 ) -CMOS_WRITE (*buf++, off); +continue ; + +guard (spinlock_irq)(&rtc_lock); +if (off <128 ) +CMOS_WRITE (*buf, off);else if (can_bank2) -cmos_write_bank2 (*buf++, off); +cmos_write_bank2 (*buf, off);else -break ; +return -EIO ; } -spin_unlock_irq (&rtc_lock); -return count ? -EIO :0 ; +return count; }/*----------------------------------------------------------------*/
Signature · 5 lines
2.47.0.163.g1226f6d8fa-goog -- Dmitry
Dnia 24 października 2024 22:37:08 CEST, Dmitry Torokhov <[email protected]> napisał/a:
Quoted 8 lines
On my device reading entirety of /sys/devices/pnp0/00:03/cmos_nvram0/nvmem takes about 9 msec during which time interrupts are off on the CPU that does the read and the thread that performs the read can not be migrated or preempted by another higher priority thread (RT or not).
Allow readers and writers be preempted by taking and releasing
rtc_lockspinlock for each individual byte read or written rather than once per read/write request.
Hello,
A nice idea!
(sorry for any formatting problems, I'm on a train right now)
Quoted 22 lines
Signed-off-by Dmitry Torokhov <[email protected]>---
drivers/rtc/rtc-cmos.c| 31 +++++++++++++++----------------1 file changed, 15 insertions(+), 16 deletions(-)drivers/rtc/rtc-cmos.c +3
-3@@ -645,18 +645,17 @@ static int cmos_nvram_read(void *priv, unsigned int off, void *val,unsigned char *buf = val; off +=NVRAM_OFFSET ; -spin_lock_irq (&rtc_lock); -for (; count; count--, off++) { +for (; count; count--, off++, buf++) { +guard (spinlock_irq)(&rtc_lock);if (off <128 ) - *buf++ =CMOS_READ (off); + *buf =CMOS_READ (off);else if (can_bank2)
drivers/rtc/rtc-cmos.c static int cmos_nvram_read(void *priv, unsigned int off, void *val, · line 658
Quoted 10 lines
drivers/rtc/rtc-cmos.c +3
-4- *buf++ =cmos_read_bank2 (off); + *buf =cmos_read_bank2 (off); else - break; + return -EIO; } -spin_unlock_irq (&rtc_lock); -return count ? -EIO :0 ; +return count;
return 0;
when you are at it.
Quoted 23 lines
drivers/rtc/rtc-cmos.c +6
-5} static int cmos_nvram_write(void *priv, unsigned int off, void *val,@@ -671,23 +670,23 @@ static int cmos_nvram_write(void *priv, unsigned int off, void *val,* NVRAM to update, updating checksums is also part of its job. */ off +=NVRAM_OFFSET ; -spin_lock_irq (&rtc_lock); -for (; count; count--, off++) { +for (; count; count--, off++, buf++) {/* don't trash RTC registers */ if (off == cmos->day_alrm || off == cmos->mon_alrm || off == cmos->century) - buf++; -else if (off <128 ) -CMOS_WRITE (*buf++, off); +continue ; + +guard (spinlock_irq)(&rtc_lock); +if (off <128 ) +CMOS_WRITE (*buf, off);else if (can_bank2)
drivers/rtc/rtc-cmos.c static int cmos_nvram_write(void *priv, unsigned int off, void *val, · line 689
Quoted 10 lines
drivers/rtc/rtc-cmos.c +3
-4-cmos_write_bank2 (*buf++, off); +cmos_write_bank2 (*buf, off); else - break; + return -EIO; } -spin_unlock_irq (&rtc_lock); -return count ? -EIO :0 ; +return count;
return 0;
Quoted 3 lines
drivers/rtc/rtc-cmos.c +0
-0}/*----------------------------------------------------------------*/
Quoted 44 lines · Mateusz Jończyk
Dnia 24 października 2024 22:37:08 CEST, Dmitry Torokhov <[email protected]> napisał/a:
Quoted 8 lines
On my device reading entirety of /sys/devices/pnp0/00:03/cmos_nvram0/nvmem takes about 9 msec during which time interrupts are off on the CPU that does the read and the thread that performs the read can not be migrated or preempted by another higher priority thread (RT or not).
Allow readers and writers be preempted by taking and releasing
rtc_lockspinlock for each individual byte read or written rather than once per read/write request.Hello,
A nice idea!
(sorry for any formatting problems, I'm on a train right now)Quoted 30 lines
Signed-off-by Dmitry Torokhov <[email protected]>---
drivers/rtc/rtc-cmos.c| 31 +++++++++++++++----------------1 file changed, 15 insertions(+), 16 deletions(-)drivers/rtc/rtc-cmos.c +5
-6@@ -645,18 +645,17 @@ static int cmos_nvram_read(void *priv, unsigned int off, void *val,unsigned char *buf = val; off +=NVRAM_OFFSET ; -spin_lock_irq (&rtc_lock); -for (; count; count--, off++) { +for (; count; count--, off++, buf++) { +guard (spinlock_irq)(&rtc_lock);if (off <128 ) - *buf++ =CMOS_READ (off); + *buf =CMOS_READ (off);else if (can_bank2) - *buf++ =cmos_read_bank2 (off); + *buf =cmos_read_bank2 (off);else -break ; +return -EIO ; } -spin_unlock_irq (&rtc_lock);
Quoted 4 lines
drivers/rtc/rtc-cmos.c static int cmos_nvram_read(void *priv, unsigned int off, void *val, · line 658
Quoted 2 lines
drivers/rtc/rtc-cmos.c +1
-1-return count ? -EIO :0 ; +return count;return 0;
Oh, yes, of course, thank you.
Signature · 1 line
Dmitry