Hi Jan, Thanks for the answer. >> From: Roman Skakun <roman_skakun@xxxxxxxx> >> >> It is possible when default IO TLB size is not >> enough to fit a long buffers as described here [1]. >> >> This patch makes a way to set this parameter >> using cmdline instead of recompiling a kernel. >> >> [1] https://www.xilinx.com/support/answers/72694.html > > I'm not convinced the swiotlb use describe there falls under "intended > use" - mapping a 1280x720 framebuffer in a single chunk? I had the same issue while mapping DMA chuck ~4MB for gem fb when using xen vdispl. I got the next log: [ 142.030421] rcar-fcp fea2f000.fcp: swiotlb buffer is full (sz: 3686400 bytes), total 32768 (slots), used 32 (slots) It happened when I tried to map bounce buffer, which has a large size. The default size if 128(IO_TLB_SEGSIZE) * 2048(IO_TLB_SHIFT) = 262144 bytes, but we requested 3686400 bytes. When I change IO_TLB_SEGSIZE to 2048. (2048(IO_TLB_SEGSIZE) * 2048(IO_TLB_SHIFT) = 4194304bytes). It makes possible to retrieve a bounce buffer for requested size. After changing this value, the problem is gone. > the bottom of this page is also confusing, as following "Then we can > confirm the modified swiotlb size in the boot log:" there is a log > fragment showing the same original size of 64Mb. I suspect, this is a mistake in the article. According to https://elixir.bootlin.com/linux/v5.14.4/source/kernel/dma/swiotlb.c#L214 and https://elixir.bootlin.com/linux/v5.15-rc1/source/kernel/dma/swiotlb.c#L182 The IO_TLB_SEGSIZE is not used to calculate total size of swiotlb area. This explains why we have the same total size before and after changing of TLB segment size. > In order to be sure to catch all uses like this one (including ones > which make it upstream in parallel to yours), I think you will want > to rename the original IO_TLB_SEGSIZE to e.g. IO_TLB_DEFAULT_SEGSIZE. I don't understand your point. Can you clarify this? >> + /* get max IO TLB segment size */ >> + if (isdigit(*str)) { >> + tmp = simple_strtoul(str, &str, 0); >> + if (tmp) >> + io_tlb_seg_size = ALIGN(tmp, IO_TLB_SEGSIZE); > > From all I can tell io_tlb_seg_size wants to be a power of 2. Merely > aligning to a multiple of IO_TLB_SEGSIZE isn't going to be enough. Yes, right, thanks! Cheers, Roman. вт, 14 сент. 2021 г. в 18:29, Jan Beulich <jbeulich@xxxxxxxx>: > > On 14.09.2021 17:10, Roman Skakun wrote: > > From: Roman Skakun <roman_skakun@xxxxxxxx> > > > > It is possible when default IO TLB size is not > > enough to fit a long buffers as described here [1]. > > > > This patch makes a way to set this parameter > > using cmdline instead of recompiling a kernel. > > > > [1] https://www.xilinx.com/support/answers/72694.html > > I'm not convinced the swiotlb use describe there falls under "intended > use" - mapping a 1280x720 framebuffer in a single chunk? (As an aside, > the bottom of this page is also confusing, as following "Then we can > confirm the modified swiotlb size in the boot log:" there is a log > fragment showing the same original size of 64Mb. > > > --- a/arch/mips/cavium-octeon/dma-octeon.c > > +++ b/arch/mips/cavium-octeon/dma-octeon.c > > @@ -237,7 +237,7 @@ void __init plat_swiotlb_setup(void) > > swiotlbsize = 64 * (1<<20); > > #endif > > swiotlb_nslabs = swiotlbsize >> IO_TLB_SHIFT; > > - swiotlb_nslabs = ALIGN(swiotlb_nslabs, IO_TLB_SEGSIZE); > > + swiotlb_nslabs = ALIGN(swiotlb_nslabs, swiotlb_io_seg_size()); > > In order to be sure to catch all uses like this one (including ones > which make it upstream in parallel to yours), I think you will want > to rename the original IO_TLB_SEGSIZE to e.g. IO_TLB_DEFAULT_SEGSIZE. > > > @@ -81,15 +86,30 @@ static unsigned int max_segment; > > static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT; > > > > static int __init > > -setup_io_tlb_npages(char *str) > > +setup_io_tlb_params(char *str) > > { > > + unsigned long tmp; > > + > > if (isdigit(*str)) { > > - /* avoid tail segment of size < IO_TLB_SEGSIZE */ > > - default_nslabs = > > - ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE); > > + default_nslabs = simple_strtoul(str, &str, 0); > > } > > if (*str == ',') > > ++str; > > + > > + /* get max IO TLB segment size */ > > + if (isdigit(*str)) { > > + tmp = simple_strtoul(str, &str, 0); > > + if (tmp) > > + io_tlb_seg_size = ALIGN(tmp, IO_TLB_SEGSIZE); > > From all I can tell io_tlb_seg_size wants to be a power of 2. Merely > aligning to a multiple of IO_TLB_SEGSIZE isn't going to be enough. > > Jan > -- Best Regards, Roman.
