> -----Original Message----- > From: Lucas Stach [mailto:dev@xxxxxxxxxx] > Sent: Friday, November 15, 2019 5:25 AM > To: Pkshih; wlanfae > Cc: linux-wireless@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx > Subject: Re: long delays in rtl8723 drivers in irq disabled sections > > Am Donnerstag, den 14.11.2019, 01:41 +0000 schrieb Pkshih: > > > -----Original Message----- > > > From: Lucas Stach [mailto:dev@xxxxxxxxxx] > > > Sent: Thursday, November 14, 2019 6:11 AM > > > To: Pkshih; wlanfae > > > Cc: linux-wireless@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx > > > Subject: Re: long delays in rtl8723 drivers in irq disabled sections > > > > > > Hi PK, > > > > > > Am Mittwoch, den 13.11.2019, 03:43 +0000 schrieb Pkshih: > > > > > -----Original Message----- > > > > > From: linux-wireless-owner@xxxxxxxxxxxxxxx [mailto:linux-wireless-owner@xxxxxxxxxxxxxxx] On > > > Behalf > > > > > Of Lucas Stach > > > > > Sent: Wednesday, November 13, 2019 5:02 AM > > > > > To: wlanfae; Pkshih > > > > > Cc: linux-wireless@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx > > > > > Subject: long delays in rtl8723 drivers in irq disabled sections > > > > > > > > > > Hi all, > > > > > > > > > > while investigating some latency issues on my laptop I stumbled across > > > > > quite large delays in the rtl8723 PHY code, which are done in IRQ > > > > > disabled atomic sections, which is blocking IRQ servicing for all > > > > > devices in the system. > > > > > > > > > > Specifically there are 3 consecutive 1ms delays in > > > > > rtl8723_phy_rf_serial_read(), which is used in an IRQ disabled call > > > > > path. Sadly those delays don't have any comment in the code explaining > > > > > why they are needed. I hope that anyone can tell if those delays are > > > > > strictly neccessary and if so if they really need to be this long. > > > > > > > > > > > > > These delays are because read RF register is an indirect access that hardware > > > > needs time to accomplish read action, but there's no ready bit, so delay > > > > is required to guarantee the read value is correct. > > > > > > Thanks for the confirmation, I suspected something like this. > > > > > > > It is possible to use smaller delay, but it's exactly required. > > > > > > 1ms seems like an eternity on modern hardware, even for an indirect > > > read. > > > > > > > For 8723be, three 1ms delays can be replaced by one 120us delay, likes > > > > @@ -89,12 +89,10 @@ u32 rtl8723_phy_rf_serial_read(struct ieee80211_hw *hw, > > (newoffset << 23) | BLSSIREADEDGE; > > rtl_set_bbreg(hw, RFPGA0_XA_HSSIPARAMETER2, MASKDWORD, > > tmplong & (~BLSSIREADEDGE)); > > - mdelay(1); > > rtl_set_bbreg(hw, pphyreg->rfhssi_para2, MASKDWORD, tmplong2); > > - mdelay(1); > > rtl_set_bbreg(hw, RFPGA0_XA_HSSIPARAMETER2, MASKDWORD, > > tmplong | BLSSIREADEDGE); > > - mdelay(1); > > + udelay(120); > > if (rfpath == RF90_PATH_A) > > rfpi_enable = (u8) rtl_get_bbreg(hw, RFPGA0_XA_HSSIPARAMETER1, > > BIT(8)); > > > > I think it'd be better. > > Yes, that looks much better. Even better would be a small comment on > how you arrived at 120us. Some internal documentation, or is this > mostly empirical? > 120us is maximum stall time with little tolerance suggested by our designer. Not only 8723be/8723de, I'll take a while to check other chips. > > > > An alternative way is to prevent calling this function in IRQ disabled flow. > > > > Could you share the calling trace? > > > > > > Sure, trimmed callstack below. As you can see the IRQ disabled section > > > is started via a spin_lock_irqsave(). The trace is from a 8723de > > > module, which is still out of tree, but the same code is present in > > > mainline and used by the other 8723 variants. > > > > By now, 8723DE will be upstream through rtw88 instead of rtlwifi. > > I haven't seen any patches for this particular chip yet. Is there any > roadmap on when we can expect this support to be added to the upstream > rtw88 driver? > 8723DE is under review internally, and it will start to be upstream at 5.5 or 5.6. > > > I don't know if this function needs to guard against something running > > > in the IRQ handler, so depending on the answer to that the solution > > > might be as simple as not disabling IRQs when taking the spinlock. > > > > > > kworker/-276 4d... 0us : _raw_spin_lock_irqsave > > > kworker/-276 4d... 0us : rtl8723_phy_rf_serial_read <-rtl8723de_phy_set_rf_reg > > > kworker/-276 4d... 1us : rtl8723_phy_query_bb_reg <-rtl8723_phy_rf_serial_read > > > kworker/-276 4d... 3us : rtl8723_phy_set_bb_reg <-rtl8723_phy_rf_serial_read > > > kworker/-276 4d... 4us : __const_udelay <-rtl8723_phy_rf_serial_read > > > kworker/-276 4d... 4us!: delay_mwaitx <-rtl8723_phy_rf_serial_read > > > kworker/-276 4d... 1004us : rtl8723_phy_set_bb_reg <-rtl8723_phy_rf_serial_read > > > [...] > > > > > > > I check TX/RX interrupt handlers, and I don't find one calls RF read function > > by now. I suspect that old code controls RF to do PS in interrupt context, so > > _irqsave version is used to ensure read RF isn't interrupted or deadlock. > > So, I change spin_lock to non-irqsave version, and do some tests on 8723BE > > that works well. > > > > What do you think about two fixes mentioned above? If they're ok, I can send > > two patches to resolve this long delays. > > Yes, both changes do make sense to me. If we can avoid an unnecessary > IRQ disable we should do so. Even then shrinking the waits to bare > minimum as required by the hardware seems to be a good thing, > especially since the wait is still done under a spinlock, so can not > use a sleeping wait. > Some callers are still in tasklet context. I'll check if it's possible to move them to work queue, but I think this isn't a short term task. PK
