Date: Sun, 29 Sep 2019 02:55:57 +0000 (UTC) From: Alexander Motin <mav@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r352861 - stable/12/sys/dev/uart Message-ID: <201909290255.x8T2tvMh082189@repo.freebsd.org>
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Author: mav Date: Sun Sep 29 02:55:57 2019 New Revision: 352861 URL: https://svnweb.freebsd.org/changeset/base/352861 Log: MFC r352369: Relax TX draining in ns8250_bus_transmit(). Since TX interrupt is generated when THRE is set, wait for TEMT set means wait for full character transmission time. At low speeds that may take awhile, burning CPU time while holding sc_hwmtx lock, also congested. This is partial revert of r317659. Modified: stable/12/sys/dev/uart/uart_dev_ns8250.c Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/dev/uart/uart_dev_ns8250.c ============================================================================== --- stable/12/sys/dev/uart/uart_dev_ns8250.c Sat Sep 28 23:08:19 2019 (r352860) +++ stable/12/sys/dev/uart/uart_dev_ns8250.c Sun Sep 29 02:55:57 2019 (r352861) @@ -1026,13 +1026,8 @@ ns8250_bus_transmit(struct uart_softc *sc) bas = &sc->sc_bas; uart_lock(sc->sc_hwmtx); - if (sc->sc_txdatasz > 1) { - if ((uart_getreg(bas, REG_LSR) & LSR_TEMT) == 0) - ns8250_drain(bas, UART_DRAIN_TRANSMITTER); - } else { - while ((uart_getreg(bas, REG_LSR) & LSR_THRE) == 0) - DELAY(4); - } + while ((uart_getreg(bas, REG_LSR) & LSR_THRE) == 0) + DELAY(4); for (i = 0; i < sc->sc_txdatasz; i++) { uart_setreg(bas, REG_DATA, sc->sc_txbuf[i]); uart_barrier(bas);
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