Date: Tue, 27 Oct 2020 21:54:08 +0000 From: bugzilla-noreply@freebsd.org To: net@FreeBSD.org Subject: [Bug 248652] iflib: netmap pkt-gen large TX performance difference between 11-STABLE and 12-STABLE/CURRENT on ix & ixl NIC Message-ID: <bug-248652-7501-0NSAWzb3A2@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-248652-7501@https.bugs.freebsd.org/bugzilla/> References: <bug-248652-7501@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D248652 --- Comment #42 from commit-hook@FreeBSD.org --- A commit references this bug: Author: vmaffione Date: Tue Oct 27 21:53:33 UTC 2020 New revision: 367093 URL: https://svnweb.freebsd.org/changeset/base/367093 Log: iflib: add per-tx-queue netmap timer The way netmap TX is handled in iflib when TX interrupts are not used (IFC_NETMAP_TX_IRQ not set) has some issues: - The netmap_tx_irq() function gets called by iflib_timer(), which gets scheduled with tick granularity (hz). This is not frequent enough for 10Gbps NICs and beyond (e.g., ixgbe or ixl). The end result is that the transmitting netmap application is not woken up fast enough to saturate the link with small packets. - The iflib_timer() functions also calls isc_txd_credits_update() to ask for more TX completion updates. However, this violates the netmap requirement that only txsync can access the TX queue for datapath operations. Only netmap_tx_irq() may be called out of the txsync context. This change introduces per-tx-queue netmap timers, using microsecond granularity to ensure that netmap_tx_irq() can be called often enough to allow for maximum packet rate. The timer routine simply calls netmap_tx_irq() to wake up the netmap application. The latter will wake up and call txsync to collect TX completion updates. This change brings back line rate speed with small packets for ixgbe. For the time being, timer expiration is hardcoded to 90 microseconds, in order to avoid introducing a new sysctl. We may eventually implement an adaptive expiration period or use another deferred work mechanism in place of timers. Also, fix the timers usage to make sure that each queue is serviced by a different CPU. PR: 248652 Reported by: sg@efficientip.com MFC after: 2 weeks Changes: head/sys/net/iflib.c --=20 You are receiving this mail because: You are on the CC list for the bug.=
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