On Thu, Dec 19, 2024 at 08:42:54PM +0800, Zhongqiu Han wrote: > It is considered good practice to call cpu_relax() in busy loops, see > Documentation/process/volatile-considered-harmful.rst. This can lower CPU > power consumption or yield to a hyperthreaded twin processor, or serve as > a compiler barrier. In addition, if something goes wrong in the busy loop > at least it can prevent things from getting worse. > > Signed-off-by: Zhongqiu Han <quic_zhonhan@xxxxxxxxxxx> > --- > drivers/tty/mips_ejtag_fdc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/mips_ejtag_fdc.c b/drivers/tty/mips_ejtag_fdc.c > index afbf7738c7c4..b17ead1e9698 100644 > --- a/drivers/tty/mips_ejtag_fdc.c > +++ b/drivers/tty/mips_ejtag_fdc.c > @@ -346,7 +346,7 @@ static void mips_ejtag_fdc_console_write(struct console *c, const char *s, > > /* Busy wait until there's space in fifo */ > while (__raw_readl(regs + REG_FDSTAT) & REG_FDSTAT_TXF) > - ; > + cpu_relax(); > __raw_writel(word.word, regs + REG_FDTX(c->index)); > } > out: > @@ -1233,7 +1233,7 @@ static void kgdbfdc_push_one(void) > > /* Busy wait until there's space in fifo */ > while (__raw_readl(regs + REG_FDSTAT) & REG_FDSTAT_TXF) > - ; > + cpu_relax(); How did you test this? Are you _sure_ it is needed at all? I think you just made these loops take a lot longer than before :( Have you had problems with these tight loops doing anything bad to your system? thanks, greg k-h
