Band by band makes sense. I shall do that instead. Thank you! :) On Mon, Nov 1, 2021 at 2:05 PM Even Rouault <[email protected]> wrote:
> Yes regarding multithreading. Regarding GRIB and performance issues, you > must be aware that the GRIB driver when accessing a single pixel of a band > needs to decompress data for the whole band. Hence there's a per-dataset > cache of band data which default to 100 MB (you can increase it by setting > the GRIB_CACHEMAX config option to a number in megabytes). So the most > performance access pattern for GRIB is to read band per band, and no > all-bands-of-a-line > Le 01/11/2021 à 21:58, Simon Eves a écrit : > > You can ignore this. > > I have rather belatedly found the documentation that says that one must > open a GDALDataset per thread, even if it's on the same file. > > The multi-threading now works just fine. > > Interestingly, we're not actually doing that with our existing geo > importer. I guess it's OK because we're pulling the OGRFeatures out with > the process thread, and only converting and loading them with the child > threads. I guess I really ought to rewrite that code too now. Sigh. > > As you were... > > Simon > > On Sun, Oct 31, 2021 at 4:27 PM Simon Eves <[email protected]> wrote: > >> We are writing a raster importer, and finding that >> GDALRasterBand::RasterIO() is unexpectedly slow for some GRIB2 files. >> >> We have a file which is about 1800x1000 pixels, with 49 bands of type >> DOUBLE. The file is about 47MB on disc. >> >> Reading all the bands of a single scanline from this file takes about >> 1300ms, which is about 26ms per band, hence the entire file takes around 20 >> minutes to import. All the time seems to be spent in the RasterIO() call, >> even though it's not doing any raster rescaling or data format conversion >> (1:1 pixels, fetching as GDT_Float64). >> >> So, I figured we'd try multi-threading it, but evidently the call is not >> thread-safe. Here is just one of various stack traces it will throw. >> >> libc.so.6!raise (Unknown Source:0) >> libc.so.6!abort (Unknown Source:0) >> libc.so.6![Unknown/Just-In-Time compiled code] (Unknown Source:0) >> libgdal.so.28!GRIBRasterBand::UncacheData(GRIBRasterBand * const this) >> (/build/scripts/gdal-3.2.2/frmts/grib/gribdataset.cpp:948) >> libgdal.so.28!GRIBRasterBand::LoadData(GRIBRasterBand * const this) >> (/build/scripts/gdal-3.2.2/frmts/grib/gribdataset.cpp:730) >> libgdal.so.28!GRIBRasterBand::LoadData(GRIBRasterBand * const this) >> (/build/scripts/gdal-3.2.2/frmts/grib/gribdataset.cpp:697) >> libgdal.so.28!GRIBRasterBand::IReadBlock(GRIBRasterBand * const this, int >> nBlockYOff, void * pImage) >> (/build/scripts/gdal-3.2.2/frmts/grib/gribdataset.cpp:803) >> libgdal.so.28!GDALRasterBand::GetLockedBlockRef(int bJustInitialize, int >> nYBlockOff, int nXBlockOff, GDALRasterBand * const this) >> (/build/scripts/gdal-3.2.2/gcore/gdal_priv.h:963) >> libgdal.so.28!GDALRasterBand::GetLockedBlockRef(GDALRasterBand * const >> this, int nXBlockOff, int nYBlockOff, int bJustInitialize) >> (/build/scripts/gdal-3.2.2/gcore/gdalrasterband.cpp:1238) >> libgdal.so.28!GDALRasterBand::IRasterIO(GDALRasterBand * const this, >> GDALRWFlag eRWFlag, int nXOff, int nYOff, int nXSize, int nYSize, void * >> pData, int nBufXSize, int nBufYSize, GDALDataType eBufType, GSpacing >> nPixelSpace, GSpacing nLineSpace, GDALRasterIOExtraArg * psExtraArg) >> (/build/scripts/gdal-3.2.2/gcore/rasterio.cpp:149) >> libgdal.so.28!GDALRasterBand::RasterIO(GDALRasterBand * const this, >> GDALRWFlag eRWFlag, int nXOff, int nYOff, int nXSize, int nYSize, void * >> pData, int nBufXSize, int nBufYSize, GDALDataType eBufType, GSpacing >> nPixelSpace, GSpacing nLineSpace, GDALRasterIOExtraArg * psExtraArg) >> (/build/scripts/gdal-3.2.2/gcore/gdalrasterband.cpp:372) >> import_export::Importer::<lambda(size_t, int)>::operator()(size_t, int) >> const(const import_export::Importer::<lambda(size_t, int)> * const >> __closure, const size_t thread_id, const int y) >> (/home/simon.eves/work/omniscidb-internal/ImportExport/Importer.cpp:5721) >> ... >> >> All of the parameters to the call are either constant or uncontended >> simple variables, and obviously there is a unique data buffer (pData) per >> thread. >> >> Is there anything we can do to make this work? >> >> I was intending to look into the lower level block-based API, in the hope >> that it will be faster, but have not yet done so. >> >> This is all with a local static build of GDAL 3.2.2 on Ubuntu 20.04 with >> GCC 9. >> >> Yours, >> >> Simon Eves >> >> -- >> <http://www.omnisci.com/> >> Simon Eves >> Senior Graphics Engineer, Rendering Group >> 100 Montgomery St (5th Floor), San Francisco, CA 94104, USA >> >> >> Email: [email protected] | Cell: +1 (415) 902-1996 >> >> > > -- > <http://www.omnisci.com/> > Simon Eves > Senior Graphics Engineer, Rendering Group > 100 Montgomery St (5th Floor), San Francisco, CA 94104, USA > > > Email: [email protected] | Cell: +1 (415) 902-1996 > > > _______________________________________________ > gdal-dev mailing > [email protected]https://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- http://www.spatialys.com > My software is free, but my time generally not. > > -- <http://www.omnisci.com/> Simon Eves Senior Graphics Engineer, Rendering Group 100 Montgomery St (5th Floor), San Francisco, CA 94104, USA Email: [email protected] | Cell: +1 (415) 902-1996
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