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linux-sg2042/drivers/tty
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Nicholas Piggin 68b2fc714f tty: hvc: hvc_poll() fix read loop batching 
Commit ec97eaad13 ("tty: hvc: hvc_poll() break hv read loop")
removes get_chars batching entirely, which slows down large console
operations like paste -- virtio console "feels worse than a 9600 baud
serial line," reports Matteo.

This adds back batching in a more latency friendly way. If the caller
can sleep then we try to fill the entire flip buffer, releasing the
lock and scheduling between each iteration. If it can not sleep, then
batches are limited to 128 bytes. Matteo confirms this fixes the
performance problem.

Latency testing the powerpc OPAL console with OpenBMC UART with a
large paste shows about 0.25ms latency, which seems reasonable. 10ms
latencies were typical for this case before the latency breaking work,
so we still see most of the benefit.

  kopald-1204    0d.h.    5us : hvc_poll <-hvc_handle_interrupt
  kopald-1204    0d.h.    5us : __hvc_poll <-hvc_handle_interrupt
  kopald-1204    0d.h.    5us : _raw_spin_lock_irqsave <-__hvc_poll
  kopald-1204    0d.h.    5us : tty_port_tty_get <-__hvc_poll
  kopald-1204    0d.h.    6us : _raw_spin_lock_irqsave <-tty_port_tty_get
  kopald-1204    0d.h.    6us : _raw_spin_unlock_irqrestore <-tty_port_tty_get
  kopald-1204    0d.h.    6us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.    7us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.    7us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.   36us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   36us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   36us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.   65us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   65us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   66us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.   94us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   95us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   95us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  124us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  124us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  125us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  154us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  154us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  154us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  183us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  184us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  184us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  213us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  213us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  213us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  242us : _raw_spin_unlock_irqrestore <-__hvc_poll
  kopald-1204    0d.h.  242us : tty_flip_buffer_push <-__hvc_poll
  kopald-1204    0d.h.  243us : queue_work_on <-tty_flip_buffer_push
  kopald-1204    0d.h.  243us : tty_kref_put <-__hvc_poll
  kopald-1204    0d.h.  243us : hvc_kick <-hvc_handle_interrupt
  kopald-1204    0d.h.  243us : wake_up_process <-hvc_kick
  kopald-1204    0d.h.  244us : try_to_wake_up <-hvc_kick
  kopald-1204    0d.h.  244us : _raw_spin_lock_irqsave <-try_to_wake_up
  kopald-1204    0d.h.  244us : _raw_spin_unlock_irqrestore <-try_to_wake_up

Reported-by: Matteo Croce <mcroce@redhat.com>
Tested-by: Matteo Croce <mcroce@redhat.com>
Tested-by: Jason Gunthorpe <jgg@mellanox.com>
Tested-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2018-09-10 18:04:31 +02:00
..
hvc tty: hvc: hvc_poll() fix read loop batching 2018-09-10 18:04:31 +02:00
ipwireless tty: ipwireless: Replace GFP_ATOMIC with GFP_KERNEL in ipwireless_network_create 2018-04-23 10:57:06 +02:00
serdev serdev: add dev_pm_domain_attach|detach() 2018-07-15 12:23:53 +02:00
serial Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
vt TTY/Serial driver patches for 4.19-rc1 2018-08-18 10:50:41 -07:00
Kconfig Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2018-04-09 09:04:10 -07:00
Makefile tty: remove bfin_jtag_comm and hvc_bfin_jtag drivers 2018-03-26 15:57:24 +02:00
amiserial.c tty: replace ->proc_fops with ->proc_show 2018-05-16 07:24:30 +02:00
cyclades.c tty: replace ->proc_fops with ->proc_show 2018-05-16 07:24:30 +02:00
ehv_bytechan.c treewide: kzalloc() -> kcalloc() 2018-06-12 16:19:22 -07:00
goldfish.c headers: separate linux/mod_devicetable.h from linux/platform_device.h 2018-07-07 17:52:26 +02:00
isicom.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
mips_ejtag_fdc.c tty: Remove redundant license text 2017-11-08 13:08:12 +01:00
moxa.c tty: moxa: Add support for CMSPAR 2017-11-28 15:32:33 +01:00
moxa.h tty: moxa: Add support for CMSPAR 2017-11-28 15:32:33 +01:00
mxser.c tty: Remove redundant license text 2017-11-08 13:08:12 +01:00
mxser.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
n_gsm.c Merge 4.17-rc3 into tty-next 2018-04-30 05:14:55 -07:00
n_hdlc.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
n_null.c tty: Remove redundant license text 2017-11-08 13:08:12 +01:00
n_r3964.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
n_tracerouter.c tty: Remove redundant license text 2017-11-08 13:08:12 +01:00
n_tracesink.c tty: Remove redundant license text 2017-11-08 13:08:12 +01:00
n_tracesink.h tty: Remove redundant license text 2017-11-08 13:08:12 +01:00
n_tty.c n_tty: Access echo_* variables carefully. 2018-06-28 21:30:16 +09:00
nozomi.c tty/nozomi: fix inconsistent indentation 2018-04-25 14:54:26 +02:00
pty.c pty: fix O_CLOEXEC for TIOCGPTPEER 2018-07-21 09:08:47 +02:00
rocket.c tty: rocket: Fix possible buffer overwrite on register_PCI 2018-08-02 10:11:32 +02:00
rocket.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rocket_int.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
synclink.c tty: replace ->proc_fops with ->proc_show 2018-05-16 07:24:30 +02:00
synclink_gt.c tty: replace ->proc_fops with ->proc_show 2018-05-16 07:24:30 +02:00
synclinkmp.c tty: replace ->proc_fops with ->proc_show 2018-05-16 07:24:30 +02:00
sysrq.c signal: Pass pid type into do_send_sig_info 2018-07-21 12:57:35 -05:00
tty_audit.c audit: eliminate audit_enabled magic number comparison 2018-06-19 10:43:55 -04:00
tty_baudrate.c tty: support CIBAUD without BOTHER 2018-07-16 12:00:43 +02:00
tty_buffer.c tty: add SPDX identifiers to all remaining files in drivers/tty/ 2017-11-08 13:08:12 +01:00
tty_io.c Merge branch 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2018-08-21 13:47:29 -07:00
tty_ioctl.c tty: add missing const to termios hw-change helper 2018-05-22 10:08:05 +02:00
tty_jobctrl.c tty: add SPDX identifiers to all remaining files in drivers/tty/ 2017-11-08 13:08:12 +01:00
tty_ldisc.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
tty_ldsem.c atomic/tty: Fix up atomic abuse in ldsem 2018-06-28 21:07:55 +09:00
tty_mutex.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
tty_port.c tty: add SPDX identifiers to all remaining files in drivers/tty/ 2017-11-08 13:08:12 +01:00
vcc.c tty: vcc: Convert timers to use timer_setup() 2017-11-04 12:01:54 +01:00