This message was previously sent to scst-devel: https://sourceforge.net/p/scst/mailman/scst-devel/thread/d381eb86-d446-4f9e-03c3-aa93d93dd074%40cybernetics.com/#msg37682919 I am using a quad-port 16 Gbps QLE2694L (ISP2071) with SCST 3.6 + qla2x00t-32gbit and kernel 5.15. The following old commit that went into upstream kernel v4.16 is causing a problem for me: commit d2b292c3f6fdef5819a276acd64915bae6384a7f Author: Quinn Tran <quinn.tran@xxxxxxxxxx> Date: Thu Dec 28 12:33:17 2017 -0800 scsi: qla2xxx: Enable ATIO interrupt handshake for ISP27XX Enable ATIO Q interrupt handshake for ISP27XX. This patch coalesce ATIO's interrupts for Quad port ISP27XX adapter. Interrupt coalesce allows performance to scale for this specific case. This commit was present in qla2xxx when qla2x00t-32gbit was first imported into SCST. With the "ATIO interrupt coalesce" enabled by the above patch, ATIO interrupts are handled by qla24xx_msix_default() rather than by qla83xx_msix_atio_q() for the ISP2071. I guess this is supposed to generate fewer interrupts so that ATIO entries can be handled in larger batches. But this causes a problem where sometimes qlt_24xx_process_atio_queue() returns while the hardware is still adding ATIO entries to the queue, but then the hardware doesn't generate another interrupt until a separate event sometimes minutes later. This leaves incoming ATIO entries (i.e. incoming target-mode SCSI commands) ignored in the adapter's hardware queue for a long time until the host sends another command at a different time to generate an interrupt. There does not seem to be any timeout function that generates an interrupt after a short period of inactivity to process the remainder of the ATIO queue, which is what would be necessary for interrupt coalesce to function properly. In my case I am using virtual tape drives, which generally process only one command at a time, so there will often never be a "next" command to generate an interrupt until the previous command completes. If the previous command is stuck in the adapter's ATIO queue, then the host will timeout and abort the command, and the task management function to abort the command generates the interrupt that causes the command to finally be received by SCST, so the command appears to have been aborted immediately. With disk drives the situation might be a bit different since a busy disk might get a steady stream of commands to generate additional interrupts to process the ATIO queue, but even that is not guaranteed, so there might still be problems. I tried to fix the problem by modifying qla24xx_msix_default() to call qlt_24xx_process_atio_queue() before wrt_reg_dword(®->hccr, HCCRX_CLR_RISC_INT) instead of after, but that didn't help. The problem was solved by disabling the ATIO interrupt coalesce feature and re-enabling the dedicated ATIO MSI-X interrupt (qla83xx_msix_atio_q()) for calling qlt_24xx_process_atio_queue(). Another workaround is to use ql2xenablemsix=0, but of course keeping MSI-X enabled is better. The patch below is against the upstream Linux kernel. It can be applied to SCST with "patch -p4" from the qla2x00t-32gbit directory. If someone really wants to keep the interrupt coalesce feature, it could be turned into a module parameter instead. >From e5888ce5dbffff2d38d9dafd4841d6d3bcda4365 Mon Sep 17 00:00:00 2001 From: Tony Battersby <tonyb@xxxxxxxxxxxxxxx> Date: Thu, 7 Jul 2022 15:08:01 -0400 Subject: [PATCH] scsi: qla2xxx: Disable ATIO interrupt coalesce for quad port ISP27XX This partially reverts commit d2b292c3f6fdef5819a276acd64915bae6384a7f. For some workloads where the host sends a batch of commands and then pauses, ATIO interrupt coalesce can cause some incoming ATIO entries to be ignored for extended periods of time, resulting in slow performance, timeouts, and aborted commands. So disable interrupt coalesce and re-enable the dedicated ATIO MSI-X interrupt. Signed-off-by: Tony Battersby <tonyb@xxxxxxxxxxxxxxx> --- drivers/scsi/qla2xxx/qla_target.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/drivers/scsi/qla2xxx/qla_target.c b/drivers/scsi/qla2xxx/qla_target.c index cb97f625970d..80fd9980dfc9 100644 --- a/drivers/scsi/qla2xxx/qla_target.c +++ b/drivers/scsi/qla2xxx/qla_target.c @@ -6932,14 +6932,8 @@ qlt_24xx_config_rings(struct scsi_qla_host *vha) if (ha->flags.msix_enabled) { if (IS_QLA83XX(ha) || IS_QLA27XX(ha) || IS_QLA28XX(ha)) { - if (IS_QLA2071(ha)) { - /* 4 ports Baker: Enable Interrupt Handshake */ - icb->msix_atio = 0; - icb->firmware_options_2 |= cpu_to_le32(BIT_26); - } else { - icb->msix_atio = cpu_to_le16(msix->entry); - icb->firmware_options_2 &= cpu_to_le32(~BIT_26); - } + icb->msix_atio = cpu_to_le16(msix->entry); + icb->firmware_options_2 &= cpu_to_le32(~BIT_26); ql_dbg(ql_dbg_init, vha, 0xf072, "Registering ICB vector 0x%x for atio que.\n", msix->entry);
