Re: [PATCH][PCI]: Introduce pci_find_capability_cached and makeMSI use it
From: Arnaldo Carvalho de Melo
Date: Thu May 15 2008 - 13:03:20 EST
Em Thu, May 15, 2008 at 01:04:26PM -0300, Arnaldo Carvalho de Melo escreveu:
> Hi,
>
> While using the preemptirqsoff ftrace tracer I noticed that
> everytime handle_edge_irq is called it needs to mask and unmask MSI, and
> that leads to a series of very expensive calls to pci_find_capability,
> as can be seen here, with preemption disabled:
>
> <idle>-0 [03] 422.558652: unmask_msi_irq <-handle_edge_irq
> <idle>-0 [03] 422.558653: msi_set_mask_bits <-unmask_msi_irq
> <idle>-0 [03] 422.558653: msi_set_enable <-msi_set_mask_bits
> <idle>-0 [03] 422.558654: pci_find_capability <-msi_set_enable
> <idle>-0 [03] 422.558655: __pci_bus_find_cap_start <-pci_find_capability
> <idle>-0 [03] 422.558655: pci_bus_read_config_word <-__pci_bus_find_cap_start
> <idle>-0 [03] 422.558656: _spin_lock_irqsave <-pci_bus_read_config_word
> <idle>-0 [03] 422.558656: add_preempt_count <-_spin_lock_irqsave
> <idle>-0 [03] 422.558657: pci_read <-pci_bus_read_config_word
> <idle>-0 [03] 422.558657: raw_pci_read <-pci_read
> <idle>-0 [03] 422.558658: pci_conf1_read <-raw_pci_read
> <idle>-0 [03] 422.558658: _spin_lock_irqsave <-pci_conf1_read
> <idle>-0 [03] 422.558659: add_preempt_count <-_spin_lock_irqsave
>
> BZZT! 37us
>
> <idle>-0 [03] 422.558696: _spin_unlock_irqrestore <-pci_conf1_read
> <idle>-0 [03] 422.558697: sub_preempt_count <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558697: preempt_schedule <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558698: _spin_unlock_irqrestore <-pci_bus_read_config_word
> <idle>-0 [03] 422.558698: sub_preempt_count <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558699: preempt_schedule <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558699: __pci_find_next_cap <-pci_find_capability
> <idle>-0 [03] 422.558700: __pci_find_next_cap_ttl <-__pci_find_next_cap
> <idle>-0 [03] 422.558700: pci_bus_read_config_byte <-__pci_find_next_cap_ttl
> <idle>-0 [03] 422.558701: _spin_lock_irqsave <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558701: add_preempt_count <-_spin_lock_irqsave
> <idle>-0 [03] 422.558702: pci_read <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558702: raw_pci_read <-pci_read
> <idle>-0 [03] 422.558703: pci_conf1_read <-raw_pci_read
> <idle>-0 [03] 422.558703: _spin_lock_irqsave <-pci_conf1_read
> <idle>-0 [03] 422.558704: add_preempt_count <-_spin_lock_irqsave
>
> BZZT! 38us
>
> <idle>-0 [03] 422.558742: _spin_unlock_irqrestore <-pci_conf1_read
> <idle>-0 [03] 422.558743: sub_preempt_count <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558743: preempt_schedule <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558744: _spin_unlock_irqrestore <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558744: sub_preempt_count <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558745: preempt_schedule <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558745: pci_bus_read_config_byte <-__pci_find_next_cap_ttl
> <idle>-0 [03] 422.558746: _spin_lock_irqsave <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558746: add_preempt_count <-_spin_lock_irqsave
> <idle>-0 [03] 422.558747: pci_read <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558747: raw_pci_read <-pci_read
> <idle>-0 [03] 422.558748: pci_conf1_read <-raw_pci_read
> <idle>-0 [03] 422.558748: _spin_lock_irqsave <-pci_conf1_read
> <idle>-0 [03] 422.558749: add_preempt_count <-_spin_lock_irqsave
>
> BZZT! 39us
>
> <idle>-0 [03] 422.558788: _spin_unlock_irqrestore <-pci_conf1_read
> <idle>-0 [03] 422.558789: sub_preempt_count <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558789: preempt_schedule <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558790: _spin_unlock_irqrestore <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558790: sub_preempt_count <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558791: preempt_schedule <-_spin_unlock_irqrestore
> <idle>-0 [03] 422.558791: pci_bus_read_config_byte <-__pci_find_next_cap_ttl
> <idle>-0 [03] 422.558792: _spin_lock_irqsave <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558792: add_preempt_count <-_spin_lock_irqsave
> <idle>-0 [03] 422.558793: pci_read <-pci_bus_read_config_byte
> <idle>-0 [03] 422.558793: raw_pci_read <-pci_read
> <idle>-0 [03] 422.558794: pci_conf1_read <-raw_pci_read
> <idle>-0 [03] 422.558794: _spin_lock_irqsave <-pci_conf1_read
> <idle>-0 [03] 422.558795: add_preempt_count <-_spin_lock_irqsave
>
> BZZT! 39us
>
> <idle>-0 [03] 422.558834: _spin_unlock_irqrestore <-pci_conf1_read
> <idle>-0 [03] 422.558834: sub_preempt_count <-_spin_unlock_irqrestore
>
> <SNIP many more such BZZT!s>
>
> So I implemented pci_find_capability_cached and made MSI use it
> for good measure, please consider applying.
>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
>
> diff --git a/Makefile b/Makefile
> index 14f34b4..d79fdac 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1,7 +1,7 @@
> VERSION = 2
> PATCHLEVEL = 6
> SUBLEVEL = 25
> -EXTRAVERSION =
> +EXTRAVERSION = .pci_cached
> NAME = Funky Weasel is Jiggy wit it
>
> # *DOCUMENTATION*
Ouch, left this in, do you want another patch or can you just remove
this bit?
Thanks,
- Arnaldo
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